Tiger beetles are predatory insects that feed on small insects and other arthropods. The adults are active, mobile predators that search and hunt for prey. The larvae, however, are passive predators. A tiger beetle larva constructs a burrow and waits at the burrow's entrance, blocking the opening with its large, sclerotized head. When a suitable prey item passes close enough, the larva jumps out and grabs the prey with its long, sickle-shaped mandibles. Hooks on the dorsal surface of the fifth abdominal segment can dig into the side of the burrow, thus preventing the larva from being pulled out by large or particularly active prey. Larvae retreat down their burrows rapidly when disturbed, and can be quite a challenge to collect!
Tiger beetles exhibit two different general life cycles. There are spring/fall species and summer species. In spring/fall species, the adult beetles emerge from pupae in the autumn and are active for a few weeks or longer, depending on annual weather conditions. As frosts occur and the weather cools, the adults hibernate for the winter. They emerge from hibernation during the spring and mate and lay eggs. Adults then usually die off, and the newly hatched larvae develop burrows and hibernate for one or more winters. When the larvae are mature, they pupate during the summer and emerge as adults in the fall, thus completing the cycle. Depending on the species, the spring/fall life cycle generally takes 2 to 4 years to complete. In summer species, adults emerge from pupae in the early summer and are active during the summer months. They mate and lay eggs during this time. Larvae hatch in the fall, develop burrows, and hibernate for the winter. The summer life cycle generally takes 1 or 2 years to complete.
Mating tiger beetle couples are often seen (and for some reason, often photographed) while collecting. Male tiger beetles can be distinguished from females by the presence of dense, thick setae on the tarsi of the foreleg. Some authors have thought that these setae are used to firmly grasp the female during copulation, but males of most species actually hold their forelegs out to the sides. Males grasp the females with their mandibles during copulation. Female tiger beetles bear grooves or coupling sulci, one sulcus on either side of the prothorax that receive the male mandibles. Males do not possess coupling sulci. During copulation, sperm is passed from the male to the female via the aedeagus which is a sclerotized organ of the male reproductive system. The shape of the aedeagus is most often different from species to species and in other beetle groups, the shape of the aedeagus is used to separate species that closely resemble one another. The male everts the aedeagus and inserts it into the vagina or vestibule of the female. Sperm passes along the aedeagus, into the vestibule, and eventually reaches the spermatheca. The spermatheca is a special organ that stores the sperm until it is ready to be used for fertilization. During oviposition (egg-laying), the mature eggs pass from the ovaries down towards the vaginal opening. Along the way, the eggs pass the spermathecal duct and are fertilized before they pass out of the body. The eight and ninth abdominal segments of the female form a telescoping ovipositor that is everted from the body and used to deposit eggs one at a time into the ground. Different species prefer different soil substrates. Females are particularly choosy about their egg-laying sites because their newly hatched larvae cannot migrate to a new site if the substrate is unsuitable for them.
After hatching, the larvae enlarge the chambers the female created during egg-laying and develop burrows. Burrows of our North Dakota species are generally 30 to 50 cm deep, but the burrows of Amblycheila cylindriformis (Say), which occurs as far north as Hot Springs, South Dakota, can be over 100 cm deep! Tiger beetle larvae develop through 3 instars over a period of 1 to 4 years (depending on the species) before pupating.
Tiger beetle species differ greatly in habitat preference. Some prefer soils with high clay content while others prefer sandy soils. Some like moist environments while others like it dry. All of our North Dakota species do like open environments, even C. sexguttata which is found along roads and open paths in moist deciduous woodlands where sunlight can penetrate. Temperature is very important to tiger beetles. As you spend time collecting tiger beetles, you will soon discover that they are most active on warm, sunny days.