Identifying Cicindelidae (Tiger Beetles)
Complete Guide to Identifying Cicindelidae (Tiger Beetles)
Introduction
The Cicindelidae, universally known as tiger beetles, represent one of the most charismatic and instantly recognizable families within the order Coleoptera. With approximately 2,600 described species distributed across all continents except Antarctica, these beetles have captured the attention of professional entomologists and amateur naturalists alike for centuries. Their combination of stunning metallic coloration, remarkable speed, conspicuous diurnal activity, and fierce predatory behavior makes them among the most engaging insects to observe and study.
Tiger beetles occupy a unique position in beetle diversity, representing one of the fastest running insects on Earth, capable of speeds exceeding 9 kilometers per hour—an extraordinary achievement for creatures measuring typically 10-20 millimeters in length. Their predatory lifestyle, habitat specificity, and sensitivity to environmental disturbance have made them valuable indicators of ecosystem health and subjects of conservation concern worldwide.
This comprehensive guide will provide you with the knowledge and skills necessary to identify tiger beetles in the field, understand their ecology and behavior, appreciate their evolutionary adaptations, and recognize their conservation significance. Whether you are a professional entomologist, conservation biologist, amateur beetle enthusiast, or simply a curious naturalist, this guide will enhance your ability to observe, identify, and understand these remarkable insects.
Family Overview and Taxonomic Position
Systematic Position and Relationships
Cicindelidae has traditionally been recognized as a distinct family within Coleoptera, though recent molecular phylogenetic studies have revealed it to be nested within the ground beetles (Carabidae). Some modern classifications now treat tiger beetles as the subfamily Cicindelinae within Carabidae, though many specialists continue to recognize family-level status due to their distinctive morphology, ecology, and behavior. For practical purposes and tradition, this guide treats them as Cicindelidae while acknowledging the close relationship with Carabidae.
Tiger beetles are classified within the suborder Adephaga, which includes predatory beetles with distinctive anatomical features including exposed trochanter segments and nototrochal respiratory system. Within Adephaga, tiger beetles represent one of the most morphologically and behaviorally specialized lineages, having evolved remarkable adaptations for cursorial (running) predation in open habitats.
Evolutionary History and Distribution
The fossil record indicates that Cicindelidae has ancient origins, with fossil tiger beetles known from Mesozoic deposits. The family achieved its greatest diversity in warm, open habitats, and their current distribution reflects both ancient vicariance patterns and more recent dispersal events. Tiger beetles inhabit diverse environments from sea level to over 4,000 meters elevation, from tropical rainforests to deserts, and from sandy beaches to alpine meadows.
Different geographic regions harbor characteristic tiger beetle faunas. North America hosts approximately 107 species in 7 genera, with the genus Cicindela particularly diverse. Australia possesses a unique fauna dominated by endemic genera. Southeast Asia represents a center of diversity for several lineages. The Neotropics harbor numerous endemic species in specialized habitats.
Primary Diagnostic Features of Cicindelidae
Overall Body Form and Proportions
Tiger beetles possess a highly distinctive body form that, once learned, allows instant recognition even at a distance. The body is typically robust yet streamlined, clearly adapted for fast running and aerial pursuit. Adults range from small species of 6-8 millimeters to large tropical species exceeding 40 millimeters, though most temperate species measure 10-20 millimeters.
The body proportions are characteristic: the head is large and bulbous, nearly as wide or wider than the prothorax, and dominated by enormous compound eyes. The prothorax is typically narrow, cylindrical or slightly constricted, clearly separated from both the head and the elytra. The elytra are usually convex and rounded, covering the abdomen entirely, creating an overall appearance of a powerful, agile predator.
When viewed from above, tiger beetles display a distinctive silhouette with the broad head, narrow prothorax, and robust elytra creating a shape unlike any other common beetle family. In lateral view, the long legs held in running position give tiger beetles an alert, ready-to-pounce appearance.
Head Structure and Eyes
The head of tiger beetles is prognathous (projecting forward horizontally) with mouthparts directed anteriorly, perfectly adapted for grasping prey while running. The most striking feature is the enormous compound eyes, which are among the proportionally largest in the insect world. These hemispherical eyes bulge prominently from the sides of the head, providing nearly 360-degree vision essential for detecting prey and predators.
The eyes are typically smooth-surfaced without setae, and their facets are numerous, providing high visual acuity. The large eye size reflects the tiger beetle’s reliance on vision for hunting, navigation, and mate recognition. Eye color varies among species, from metallic green or copper to dark brown or black, and can provide identification clues.
Between the eyes lies the frons (forehead region), which may be smooth, punctate, or rugose. The shape and sculpture of this area, along with the presence or absence of setae, can be diagnostic at the species level. Some species have distinctive markings or coloration on the frons.
The antennae are filiform (thread-like), moderately long, and arise from between the eyes and mandibles. They are typically 11-segmented and covered with sensory setae. Antennal length and the proportions of individual segments vary among genera and can aid identification.
Mandibles: The Tiger’s Fangs
Tiger beetle mandibles are among their most remarkable features and the source of their common name. These sickle-shaped, sharply pointed, and often curved structures project prominently forward from the head, clearly visible even in undisturbed beetles. The mandibles are disproportionately large for the beetle’s size, adapted for piercing and grasping fast-moving prey.
Each mandible typically bears several teeth along its inner margin, with a large apical tooth at the tip and smaller subapical teeth toward the base. The number, size, and arrangement of these teeth vary among species and can be taxonomically important. The mandibles may be metallic green, copper, black, or bicolored, and this coloration can be species-specific.
Sexual dimorphism in mandible size is common, with males often possessing larger, more curved, or more elaborately toothed mandibles than females. In some species, male mandibles are so enlarged that they cross over each other when closed. These enlarged mandibles function in male-male combat during territorial disputes and in grasping females during mating.
The mandibular musculature is correspondingly powerful, allowing tiger beetles to generate impressive bite force relative to their size. The bite of large tropical species can pierce human skin, though temperate species are generally incapable of biting humans effectively due to their small size.
Thorax and Prothorax
The prothorax (first thoracic segment) of tiger beetles is distinctive in form. It is typically cylindrical, narrower than the head and elytra, and often constricted or narrowed at the anterior and posterior ends. This hour-glass or barrel-shaped configuration is characteristic of the family.
The pronotum (dorsal surface of the prothorax) may be smooth and shining or variously sculptured with punctures, grooves, or rugosities. Lateral margins may be simple, margined with a fine raised edge, or expanded. The anterior margin often curves forward to accommodate the head, while the posterior margin may be straight, curved, or sinuate.
Many species have distinctive pronotal markings including lateral white or metallic spots, median longitudinal stripes, or marginal bands. The presence, size, shape, and color of these markings are important identification characters, though they can be variable within species.
The prosternum (underside of the prothorax) typically has a prosternal process that projects backward between the front coxae. The shape of this process varies among genera and can be a useful identification character, though it requires examination of the beetle’s underside.
The mesothorax and metathorax are fused and hidden beneath the elytra. The scutellum, a small triangular plate visible at the base of the elytra between their inner margins, is typically present but small.
Elytral Characteristics
The elytra (hardened forewings) of tiger beetles are typically convex, rounded at the shoulders and apex, and completely cover the abdomen. Elytral shape varies from nearly parallel-sided to distinctly ovoid, and this overall shape is often genus- or species-specific.
The elytral surface may be smooth and highly polished, finely punctate, or more coarsely sculptured. Some species have faint longitudinal striations or grooves, while others are essentially smooth. Surface microsculpture, visible under magnification, creates the metallic or iridescent colors characteristic of many species.
Tiger beetles are justly famous for their brilliant metallic coloration. Colors include various shades of green, blue, copper, bronze, purple, and violet, often with spectacular iridescence that changes with viewing angle. The structural coloration results from microscopic surface structure diffracting light rather than from pigments, explaining the metallic sheen.
Elytral maculation (pattern of markings) provides crucial identification characters. Many species have white, cream, yellowish, or pale markings on the elytra. These markings typically consist of:
- Humeral lunule: a curved mark near the shoulder (anterior lateral portion)
- Middle band: a transverse or angled band across the middle of the elytra
- Apical lunule: a curved mark near the elytral apex
The presence, absence, size, shape, connectivity, and color of these markings are diagnostic. Some species have complete bands connecting across the suture, others have isolated spots or lunules, and some lack markings entirely. Intraspecific variation in maculation is common, with some species exhibiting polymorphism ranging from heavily marked to nearly immaculate individuals.
The elytral apex may be rounded, truncate, or slightly emarginate. Fine setae or spines along the apical margin are present in some groups. The elytral suture (where left and right elytra meet) is typically straight and tightly closed.
Legs: Built for Speed
Tiger beetle legs are long, slender, and clearly adapted for rapid running. All three pairs of legs are similar in form, unlike many beetles where the hind legs are modified for jumping or swimming. The legs are typically brightly colored, often metallic green, blue, or copper matching the body, though some species have contrastingly colored leg segments.
The coxae (basal leg segments) are large and prominent, particularly the front coxae which are globular and project prominently from the body. The trochanters are elongate and exposed (not hidden within the coxae), a characteristic feature of Adephaga.
The femora (thigh segments) are robust and muscular, housing the powerful muscles that generate the tiger beetle’s impressive running speed. Femoral coloration and any markings or banding can be diagnostic.
The tibiae (shin segments) are long and slender, often with two rows of spines along their length. These spines provide traction on various substrates. The number, size, and arrangement of tibial spines can vary among species. The apex of each tibia typically bears two spurs.
The tarsi (feet) are 5-segmented on all legs, with the first four segments usually bearing dense brushes of setae on the underside. These setae increase surface contact for traction during high-speed running. The fifth tarsal segment is elongate and bears two curved claws at its apex.
Sexual dimorphism in leg structure is common, with males often having the first three tarsal segments of the front legs expanded and covered with dense adhesive setae on the underside. These expanded tarsi function in grasping the female’s smooth elytra during mating. The degree of expansion varies among species and can aid in sex determination.
Ventral Surface
The underside of tiger beetles is typically less ornately colored than the dorsum, often metallic green, blue, copper, or dark with metallic reflections. The ventral surface may be glabrous (smooth and shiny) or covered with fine white or colored pubescence.
The thoracic sternites (ventral plates) are sclerotized and typically smooth or punctate. The mesepisternum and metepisternum (lateral thoracic plates) are visible from below and may bear distinctive sculpture or pubescence patterns.
The abdomen consists of six visible sternites in both sexes (the number of tergites visible from above may differ). The sternites may be smooth, punctate, or pubescent. The last visible sternite (anal sternite) may show sexual dimorphism in shape or sculpture.
Male genitalia are often extruded in dead or preserved specimens, visible at the abdominal apex. Female ovipositors are typically retracted but may be visible in some specimens.
Generic and Species-Level Identification
Major Genera of North America
Cicindela (now often split into multiple genera including Cicindelidia, Cylindera, Ellipsoptera, and others): This genus complex contains the majority of North American tiger beetle species. Members are typically 10-15 mm long, with relatively broad, convex elytra. Coloration ranges from brilliant metallic green, blue, or copper to drab brown or black. Elytral maculation is highly variable, with different patterns characterizing different species. Species occupy diverse habitats from beaches to grasslands to forest paths.
Cicindelidia: Split from Cicindela, this genus includes species like the six-spotted tiger beetle (C. sexguttata), one of North America’s most common and recognizable tiger beetles. Members typically have brilliant metallic green elytra with white marginal markings. They frequently inhabit woodland paths and are among the most shade-tolerant tiger beetles.
Tetracha: Large, robust tiger beetles (15-25 mm) with a distinctive appearance. The head and prothorax are typically narrower relative to the broad, convex elytra compared to Cicindela. Most species are uniformly colored without elytral maculation, in shades of green, violet, bronze, or black. Tetracha carolina and T. virginica are widespread eastern species. These beetles are typically nocturnal or crepuscular, unlike most tiger beetles.
Amblycheila: The giant North American tiger beetles, with some species exceeding 30 mm. These impressive beetles have a massive head with enormous mandibles, robust build, and uniformly black coloration without metallic sheen. They are nocturnal and flightless, with the elytra fused along the suture. Amblycheila species inhabit arid and semi-arid regions of western North America, where they hunt at night for large arthropod prey.
Habroscelimorpha: Split from Cicindela, this genus includes beach-dwelling species adapted to coastal habitats. Species are typically robust with relatively short legs. The back beach species H. dorsalis dorsalis is endangered, restricted to Atlantic coastal beaches.
Dromochorus: Small tiger beetles (6-10 mm) with distinctive habitat preferences. Most species are associated with forest habitats, often found along shaded streams or in woodland clearings. They are less boldly marked than many Cicindela species and are often overlooked due to small size and secretive habits.
Tropical and Subtropical Genera
Manticora: African tiger beetles representing some of the largest cicindelids, with some species exceeding 60 mm. These impressive beetles are flightless with fused elytra, uniformly black or dark brown, and possess enormous mandibles. They are primarily nocturnal predators of other large arthropods and inhabit savannas and arid regions.
Megacephala: Tropical tiger beetles typically larger than temperate Cicindela species, with particularly large heads and prominent eyes. Many species are brilliant metallic green, blue, or multicolored. They inhabit various tropical habitats from rainforest edges to open grasslands. The genus is diverse in Africa, Asia, and the Americas.
Collyris: A distinctive genus of primarily arboreal tiger beetles from Southeast Asia and surrounding regions. Members have an extremely elongate, slender body form unlike typical tiger beetles, with very long legs and antennae. They hunt on tree trunks and large leaves, representing a different ecological niche than most ground-dwelling cicindelids.
Tricondyla: Another arboreal genus from tropical Asia, Tricondyla species have an elongate, flattened form adapted to life on tree bark. They are typically brown or black with reduced metallic coloration, providing camouflage against bark. Their hunting behavior is adapted to the vertical substrate of tree trunks.
Oxycheila: Neotropical tiger beetles with distinctive elongate, flattened form. Many species are associated with riverine or wetland habitats. Coloration is typically metallic green, blue, or copper, often with bold white or yellow elytral markings.
Key Characters for Species Identification
Elytral Maculation Patterns: The arrangement of pale markings on the elytra provides primary species-level identification characters. Note the presence, position, size, shape, and connectivity of humeral, middle, and apical markings. Sketch or photograph the pattern from directly above for comparison with identification guides.
Color and Metallic Sheen: Body color, including the specific shade of metallic green, blue, copper, or other coloration, can be diagnostic. Note whether coloration is uniform or varies across body regions. Record whether color changes noticeably with viewing angle (iridescence).
Body Size and Proportions: Measure total body length and note relative proportions of head, prothorax, and elytra. Are the elytra distinctly broader than the prothorax, or is the transition more gradual? Is the body slender and parallel-sided or broad and convex?
Pronotal Shape and Sculpture: Examine the prothorax shape and any sculpture, punctation, grooves, or markings present. Note the presence of lateral pronotal spots or markings and their size and position.
Labral Characteristics: The labrum (upper lip) is visible between the mandible bases when viewed from the front. Its color (often white, pale, or contrasting with head color), shape, and the number of marginal teeth or setae can be diagnostic.
Leg Coloration: Note leg color and any distinctive banding or color patterns on femora or tibiae.
Geographic Location: Many tiger beetle species have restricted ranges. Knowing which species occur in your area greatly narrows identification possibilities.
Habitat and Substrate: Different species prefer different substrates (sand, clay, salt flats, gravel) and habitats (beaches, prairies, forest paths). Habitat preference is often genus- or species-specific.
Seasonal Occurrence: Many tiger beetles have specific emergence periods and flight seasons. Spring species, summer species, and fall species differ in many regions.
Detailed Ecology and Natural History
Habitat Preferences and Substrate Specialization
Tiger beetles exhibit remarkable habitat specificity, with different species specialized for different substrate types and environmental conditions. This specialization reflects adaptations in leg morphology, coloration, thermal tolerance, and larval biology.
Sandy Habitats: Many tiger beetle species specialize on sandy substrates. Beach species occupy ocean, lake, and river beaches, often showing vertical zonation with different species at different distances from the water. Species like Habroscelimorpha dorsalis inhabit upper beach zones, while others occupy lower beach areas or sand bars. Dune species inhabit shifting or stabilized dunes, often in arid or semi-arid regions.
Sandy substrate specialists typically have legs adapted for traction on loose sand, often with longer tibial spines. Coloration often matches sand color for camouflage. Larvae construct burrows in sand stabilized by moisture or roots, and adults are active during cooler periods to avoid overheating on hot sand.
Clay Substrates: Clay specialists inhabit clay banks, badlands, eroded slopes, and hard-packed clay soils. These habitats often support distinctive species not found on sand. The clay specialists typically have darker coloration, and their larvae must construct burrows in harder substrate requiring different digging adaptations.
Species like Cicindela punctulata inhabit clay paths and roads, while others specialize on eroding clay banks or exposures. The substrate hardness influences larval distribution and adult foraging patterns.
Saline and Alkaline Habitats: Salt flat specialists occupy alkali flats, salt marshes, and saline seeps in arid regions. These habitats support unique tiger beetle assemblages adapted to high salinity and often sparse vegetation. Species like Cicindela togata inhabit salt flats across western North America.
These specialists tolerate high salinity both as adults and larvae. Their prey communities consist of salt-tolerant arthropods, and their emergence patterns often coincide with seasonal moisture availability in these harsh environments.
Forest Habitats: Woodland species represent a distinct ecological group, adapted to shaded or partially shaded conditions. They typically have darker coloration (often lacking metallic sheen or being dark bronze/black) and are less dependent on high temperatures for activity than open habitat species.
Woodland path species like Cicindelidia sexguttata follow paths, roads, and clearings through forests, foraging on the path surface. They tolerate lower temperatures and lower light levels than prairie or beach species. Deep forest species are less common but include some Dromochorus species inhabiting shaded stream banks.
Riparian and Wetland Habitats: Riverbank, stream edge, and wetland specialists occupy moist substrates adjacent to water. These species often have specific moisture requirements and may be active during cooler, cloudier conditions than species from xeric habitats.
Some species specialize on unvegetated mud or sand along streams, while others inhabit vegetated wetland margins. Larval burrows may be in periodically inundated substrates, requiring adaptations to temporary flooding.
Grassland and Prairie: Open grassland species occupy natural prairies, disturbed grasslands, overgrazed pastures, and similar open habitats with sparse to moderate vegetation. These species typically require areas with exposed soil for larval burrows and adult foraging.
Prairie specialists have declined dramatically with prairie habitat loss, making some species endangered. They require fire or grazing to maintain sparse vegetation and exposed soil, and fire suppression has harmed many populations.
Alpine and Montane Habitats: Mountain specialists occupy alpine meadows, mountain streams, and high-elevation habitats. These species are adapted to short growing seasons, cold temperatures, and high UV exposure at elevation.
Some alpine species emerge for only brief periods during summer, completing their entire above-ground life cycle in a few weeks. Others may require multiple years for larval development in the harsh alpine environment.
Adult Behavior and Activity Patterns
Visual Predation and Hunting Behavior: Tiger beetles are primarily visual predators, relying on their enormous eyes to detect prey movement. They typically employ a sit-and-wait strategy, pausing frequently while patrolling their territory to scan for prey. When prey is detected, they pursue with explosive acceleration, running down their prey with remarkable speed.
During high-speed pursuit, tiger beetles may actually run so fast that they temporarily outpace their visual processing ability, forcing them to stop momentarily to reacquire their prey visually before continuing pursuit. This stop-and-go chase behavior is characteristic and easily observed.
Prey capture involves grasping the prey with the large mandibles and manipulating it with the palps and forelegs. Tiger beetles are generalist predators, taking any arthropod prey of appropriate size including flies, ants, caterpillars, spiders, and other beetles. They may consume prey on the spot or carry it to a sheltered location.
Thermoregulation and Activity Periods: As ectothermic insects, tiger beetles depend on environmental temperature for activity. Most species are active during warm, sunny conditions, and different species have different thermal optima. Some species are active at cooler temperatures than others, allowing temporal resource partitioning.
Tiger beetles thermoregulate behaviorally, adjusting body orientation relative to the sun, seeking shade when overheated, and basking when cool. On very hot substrates, they may perform “stilting” behavior, extending their long legs to lift the body high above the hot ground and reduce heat gain.
On extremely hot days, many species cease activity during midday, showing bimodal activity peaks in morning and afternoon. Others may be active only during morning hours. Some species are crepuscular or nocturnal, avoiding the heat of day entirely.
Territorial Behavior: Many tiger beetle species are territorial, with individuals defending foraging areas against conspecifics. Territories may be small, just a few square meters, and individuals patrol regularly. When another tiger beetle intrudes, aggressive interactions ensue.
Territorial disputes may involve displays such as body raising, mandible gaping, or head bobbing. More serious encounters involve charging, chasing, and physical contact. Males are typically more territorial than females, and territories may provide access to both foraging resources and mating opportunities.
Flight Behavior: Most tiger beetles are strong fliers, using flight for dispersal, escape from predators, and sometimes foraging. Flight is typically initiated by rapid running takeoff, with the beetle gaining speed before taking wing. Some species fly readily, while others fly only when necessary.
Flight distances vary from short hops of a few meters to sustained flights covering hundreds of meters. Some species undertake seasonal migrations or dispersal flights. Flight activity is temperature-dependent, with most species flying only during warm conditions.
Some tiger beetle groups have independently evolved flightlessness, with fused elytra and reduced or absent hind wings. Flightless species include the large Amblycheila and Manticora species, which compensate for flightlessness with impressive running ability and typically nocturnal habits reducing predation risk.
Mating Behavior: Tiger beetle mating begins with male pursuit of females. Males patrol territories and pursue any potential mate encountered. Courtship may involve the male approaching the female from behind and touching her with his antennae and palps.
Mating involves the male mounting the female’s back and grasping her smooth elytra with his expanded front tarsi. His aedeagus extends and connects with the female’s reproductive opening at the abdominal apex. Mating may last from a few minutes to several hours.
Males may mate multiple times, while females typically mate once or a few times. In some species, male-male competition is intense, with males interrupting copulating pairs and attempting to displace the mounted male. Female choice may occur, with females rejecting some males.
Oviposition and Egg-Laying: After mating, females search for suitable oviposition sites. Site selection involves assessment of substrate type, moisture level, temperature, and possibly prey availability for larvae. The female digs a shallow pit or creates a small burrow with her mandibles and forelegs, deposits a single egg, and covers it with soil.
Females may lay 30-100 or more eggs over their lifetime, distributing them across suitable habitat rather than concentrating them. Eggs are typically laid singly, reducing sibling competition and predation risk. Egg-laying continues over days to weeks, with females periodically foraging to obtain nutrients for egg production.
Larval Biology and Development
Larval Morphology: Tiger beetle larvae are bizarre-looking creatures, utterly different in appearance from adults. The larvae are C-shaped grubs with a large, heavily sclerotized head capsule, powerful mandibles, and a soft, curved abdomen. The body is distinctly divided into head, thorax, and abdomen.
The head capsule is large, often nearly as wide as the body, and heavily armored with thick sclerotization. The mandibles are large, curved, and sharply pointed, adapted for grasping prey. The eyes are reduced to simple ocelli providing minimal vision, reflecting the larval dependence on tactile and chemical cues rather than vision.
The thorax bears three pairs of legs with curved claws for gripping the burrow walls. The abdomen is soft, pale, and curved, with the fifth abdominal segment bearing a characteristic dorsal hump or protuberance. This hump bears forward-projecting hooks that anchor the larva in its burrow, preventing prey from pulling the larva out while also allowing the larva to rapidly retreat when threatened.
The last abdominal segment is equipped with cerci and other projections that may assist in burrow excavation and provide sensory information. The entire larva is beautifully adapted for its specialized life as an ambush predator in a vertical burrow.
Burrow Construction and Structure: Tiger beetle larvae construct vertical burrows in soil or sand, with burrow depth varying from a few centimeters to over a meter depending on species, soil type, and larval instar. First-instar larvae construct shallow burrows, while mature third-instar larvae create deep burrows extending well below the soil surface.
The burrow is precisely circular in cross-section, with the diameter exactly matching the larval head capsule width. This ensures the larva can completely block the burrow entrance with its head capsule, creating an effective trap for passing prey.
Burrow construction involves using the mandibles and legs to excavate soil, which is carried up the burrow and deposited at the surface, often creating a small mound or crater around the burrow entrance. The burrow walls may be smoothed and consolidated by the larva pressing against them as it moves up and down.
In sandy or loose soil, the burrow may collapse and require reconstruction after rain or disturbance. In clay or consolidated soil, burrows may be more permanent. Some species create a slight funnel or crater at the entrance, which may help funnel prey toward the waiting larva.
Ambush Predation Strategy: The larval hunting strategy is entirely different from the active cursorial predation of adults. Larvae are ambush predators, remaining stationary at the burrow entrance with the head capsule positioned flush with the soil surface, creating an nearly invisible trap.
The larval posture at the entrance involves the body curved in the burrow with the legs gripping the walls and the abdominal hooks anchoring against the burrow sides. The head is positioned with mandibles closed, creating a flat platform at the burrow entrance. The larva remains motionless, relying on vibration and contact detection to sense approaching prey.
When prey (typically a small arthropod) steps onto or near the larval head capsule, the larva reacts with explosive speed, opening its mandibles and grasping the prey. The large mandibles with their sharp, curved teeth efficiently pierce and hold prey. The larva then drags the prey into the burrow to consume it safely underground.
If a prey item is too large or strong, struggling prey may threaten to pull the larva from its burrow. The abdominal anchor hooks prevent this, allowing the larva to maintain position while subduing prey. If danger threatens (such as a parasitoid wasp or predator), the larva can instantly retreat deep into its burrow.
Development and Growth: Tiger beetle larvae undergo three instars, each progressively larger and occupying deeper burrows. Each instar is separated by a molt, during which the larva retreats into its burrow and remains inactive.
Development time varies greatly among species and depends on temperature, prey availability, and other factors. Some species complete development in one year with larvae present year-round. Others have two-year or three-year life cycles, with larvae overwintering in their burrows in temperate regions.
During winter in temperate climates, larvae plug their burrow entrances and retreat to the burrow base where they enter diapause (dormancy). They resume activity and feeding when temperatures warm in spring.
Third-instar larvae, when fully grown and after accumulating sufficient resources, cease feeding and construct a pupal chamber at the base of their burrow. This chamber is enlarged and smoothed, providing space for pupation.
Pupation and Adult Emergence: Pupation occurs in the pupal chamber underground. The pupa is initially soft and pale, gradually hardening and developing adult coloration. The pupal stage typically lasts 2-3 weeks depending on temperature.
After emerging from the pupal skin, the teneral adult remains underground for days to weeks, allowing the exoskeleton to fully harden and coloration to develop. The adult then digs upward, emerging from the burrow entrance.
Emergence timing is often synchronized within populations, resulting in large numbers of adults appearing simultaneously. This synchrony may overwhelm predators and facilitate mating. Different species have different emergence periods, with some emerging in spring, others in summer, and some species having fall emergences.
Predators, Parasites, and Defense Mechanisms
Vertebrate Predators: Tiger beetles, despite their speed and wariness, fall prey to various vertebrate predators. Birds are major predators, with species like robins, bluebirds, and bee-eaters capturing tiger beetles. The beetles’ metallic coloration may make them conspicuous to birds, though their speed and flight ability provide escape options.
Lizards in warm climates prey on tiger beetles, using their own speed and visual acuity to capture these agile insects. Small mammals including rodents may occasionally consume tiger beetles, though they are probably not preferred prey due to their hard exoskeleton.
Tiger beetles employ several anti-predator strategies including rapid running, flight, wariness (fleeing when approached), and cryptic behavior (freezing when threatened). Their hard exoskeleton provides protection against some predators. Some species may release defensive secretions when captured, though this is less developed than in related ground beetles.
Robber Flies and Predatory Insects: Large predatory insects present significant predation pressure on tiger beetles. Robber flies (Asilidae) are visual predators that hunt on the wing, capturing flying tiger beetles in mid-air. The flies’ speed, agility, and powerful piercing mouthparts allow them to overcome tiger beetles.
Other tiger beetles may prey on smaller tiger beetle species or individuals, practicing intraguild predation. Predatory ground beetles (Carabidae) may encounter and attack tiger beetle larvae in their burrows or terrestrial adults.
Parasitoids: Various parasitoid wasps and flies attack tiger beetle larvae in their burrows. These parasitoids have evolved specialized behaviors to overcome the larvae’s defensive retreat behavior. Some wasps are extremely small, entering the larval burrow to oviposit on the larva. Others may dig beside burrows to access larvae.
Bombyliid flies (bee flies) hover above larval burrows and flick eggs toward the entrance. Hatching bee fly larvae enter the burrow and parasitize the tiger beetle larva. Mutillid wasps (velvet ants) may parasitize tiger beetle larvae or pupae, with females digging to access underground life stages.
Parasitism rates can be high in some populations, significantly impacting recruitment. Some tiger beetle species may have co-evolved with specific parasitoids, resulting in host-parasitoid dynamics influencing population cycles.
Pathogens: Tiger beetles are susceptible to various pathogens including fungi, bacteria, and viruses. Entomopathogenic fungi may infect adults or larvae, particularly in humid conditions. Bacterial and viral diseases can cause mortality, though these are less studied in tiger beetles than in some other insect groups.