Description & Statistics
These giant water bugs are cosmopolitan in temperate and tropical areas. Some species reach 80 mm in length. Important morphological characters include flattened legs; hind tarsi with two apical claws; fore legs adapted for grasping prey, the femora enlarged and the tibiae curved; ocelli absent; antennae shorter than the head, inserted beneath the eyes.
All of the Belostomatidae are predaceous. They are entirely aquatic as nymphs and pass much time under water as adults. Adults of some species are active fliers and are frequently attracted to lights. Females of some species lay their eggs on the back of the male, which carries them about until they hatch. Belostomatidae feed on a variety of pond life, including insects, and in the case of larger species, small vertebrates, e.g., fish and tadpoles. Sometimes they are harmful in pond cultures of small fish. They may also inflict a painful bite to humans. The family has not been used directly in biological control, although their predatory activity on mosquitoes may contribute to natural control of the latter (Cummings 1933, Usinger 1963).
Behavior & Ecology
This is a family of insects in the order Hemiptera, known as giant water bugs or colloquially as toe-biters, electric-light bugs and Alligator Ticks (in Florida). They are the largest insects in the order Hemiptera, and occur worldwide, with most of the species in North America, South America and East Asia. They are typically encountered in freshwater streams and ponds. Most species are relatively large (2 cm or more) with some of the largest, such as Lethocerus, exceeding 12 cm, and nearly reaching the dimensions (length and mass) of some of the larger beetles in the world. Giant water bugs are a popular food in Thailand.
Bugs of the family Belostomatidae are fierce predators which stalk, capture and feed on aquatic crustaceans, fish and amphibians. They often lie motionless at the bottom of a body of water, attached to various objects, where they wait for prey to come near. They then strike, injecting a powerful digestive saliva with their mandible, and sucking out the liquefied remains. Their bite is considered one of the most painful that can be inflicted by any insect (the Schmidt Sting Pain Index excludes insects other than Hymenoptera); the longer the bug is allowed to inject its saliva, the worse the resulting bite, and as the saliva liquefies muscle tissue, it can in rare instances do permanent damage. Adults cannot breathe under water, and must surface periodically for air. Occasionally when encountered by a larger predator, such as a human, they have been known to "play dead" and emit a fluid from their anus. Due to this they are assumed dead by humans only to later "come alive" with painful results.
Belostomatids show paternal care and the eggs of many species are laid on the male's wings and carried until they hatch. The male cannot mate during this period. The males invest considerable time and energy in reproduction and females take the role of actively finding males to mate. This role reversal matches the predictions of R. L. Trivers' parental investment theory.
In some areas belostomatids are considered a delicacy, and can be found for sale in markets. They are often collected for this purpose using large floating traps on ponds, set with black lights to attract the bugs. Adults fly at night, like many aquatic insects, and are attracted to lights during the breeding season.
Males attract the females doing a series of periodic movements near water surface generating ripples in the water known as display pumping. An accompanying low frequency acoustical signal has been observed in at least one species of Belostomatinae. Before a female begins ovipositing the eggs, she mates with the male. Then a series of intercalated matings and ovipositions occur, females ovipositing 1-4 eggs in each ovipositing bout. An egg batch can have more than 100 eggs so a couple may copulate more than 30 times before female oviposits all the egg batch. This increases male confidence of paternity, a condition thought necessary for the origin of paternal care. There are two substrates of oviposition, females of species pertaining to the ancestral subfamily (Lethocerinae) oviposit on emergent vegetation. On the other hand, Belostomatinae females oviposit on the males' dorsum. The male will raise the eggs exposing them to air periodically to discourage the growth of fungus and maintain the viability of the eggs, or conduct a series of movements below the water known as brood pumping that increases the amount of oxygen diffusion. The eggs will hatch in approximately three weeks but their hatching time will decrease as temperature rises.
Cummings, C. 1933. Bull. Univ. Kansas 34: 197-219.
Usinger, R. L. 1963. Aquatic Insects of California. Univ. Calif. Press, Berkeley. p. 203-06.