Comprehensive DescriptionRead full entry
Genus Scapteriscus (two-clawed mole crickets) in North America north of Mexico
Members of this genus have two blade-like claws (dactyls) on each foretibia and the auditory tympanum is exposed. The foretrochanter is armed with an elongate blade. The hindtibia has 3-6 long spines along its upper inner margin.
Our three species in this genus are native to South America and first became established in North America more than 90 years ago, apparently from stowaways in ships' ballast. Maps of when and where they were introduced and how they spread are on the species pages and in Walker & Nickle (1981).
Two-clawed mole crickets require a year or less for a generation. In the colder parts of their ranges they overwinter both as adults and large nymphs. Eggs are laid in clutches of 25 to 60 in small ovoid chambers (4 x 3 cm) 9 to 30 cm below the surface.
Members of this genus are the most damaging crickets in the New World. In the southeastern United States tawny mole crickets (S. vicinus) are major pests of established lawns and pastures, causing annual losses of $10's of millions. Short-winged mole crickets (S. abbreviatus) do the same type of damage but are much more restricted geographically. Southern mole crickets (S. borellii) feed largely on animal matter and avoid established turf; however, they damage seedlings in newly planted lawns, gardens, and fields.
Because our pest mole crickets were introduced and occurred in much greater numbers here than in their homeland, University of Florida researchers concluded that they might be controlled by classical biological control--that is, by introducing natural enemies that had been left behind when they immigrated from South America. Of the enemies that proved promising because of their host specificity, three have been successfully introduced, and have substantially reduced Scapteriscus populations. Steinernema scapterisci is a nematode that kills mole crickets by introducing lethal microbes (Parkman et al 1993). Ormia depleta is a tachinid fly that homes on the calling songs of male mole crickets and deposits living larvae that enter and consume mole crickets (Frank et al 1996). Larra bicolor is a sphecid wasp that chases a mole cricket from its burrow, subdues it with a sting and glues an egg at the base of a middle leg. The mole cricket recovers but the egg becomes a larva that feeds on the cricket while attached externally and eventually kills its host and consumes the remains (Walker 1984).
Large numbers of tawny and southern mole crickets fly during the early evening of warm days each spring. One result of such flights is that new lawns and fields are infested and pesticide-treated ones are re-infested. Another result is that females find mates by homing to the appropriate calling song and landing near the entrance to the caller's burrow.
Some important features of the flights are not adequately understood. Males and mated females, as well as virgin females, often terminate their flights by homing to conspecific calling song, and the same individual may fly and home repeatedly over a period of several weeks. Available evidence suggests that many flights terminate near their starting points and that in heavily infested fields a minority of the males call each evening. Pair formation and sexual competition in these species deserve further study. Most flights probably involve more than colonizing new or better fields or finding a willing source of conspecific sperm. T.G. Forrest (1983) has shown that calling males vary greatly in their attractiveness to females. On an evening when one calling male attracts no female, another, calling nearby, may attract more than 20! (He cannot service so many--Forrest prevented them from reaching the male.) Male attractiveness correlates with loudness of the calling song. Loudness correlates with both male size and soil moisture, which in turn are indicative of male quality and habitat quality. Scientists have exploited the attractiveness of loud calls by broadcasting simulated mole cricket sounds more than 30 times as powerful as the loudest male and have collected as many as 8000 mole crickets at a single sound source in a single evening.