Scientific Name: Gryllus pennsylvanicus
Common Name: Field Cricket
(Information for this species page was gathered in part by Alicia Fitzgerald for the Spring 2006, Biology 220W at Penn State New Kensington)
The field cricket (Gryllus pennsylvanicus) is found abundantly in a great variety of habitats (including fields and lawns, forest edges, mature forests, caves, damp basements, around plumbing, and even in outhouses) and occurs over a wide geographic range which includes most of the eastern and midwestern United States north of Florida. This wide range of habitat selection is reflective of the species’ extremely broad tolerance ranges to key environmental factors. In natural habitats, G. pennsylvanicus may be found in shallow burrows and also in the matrix of dead or living vegetation above the level of the soil.
Adult field crickets are black and brown in color and are between one half and one inch long. They have six legs, long antennae, and prominent cerci at the end of their abdomens. Their hindmost legs are very enlarged and are used by the cricket for powerful and rapid jumping. The hind wings of the field cricket are large and brightly pigmented. Not all field cricket individuals, though, are capable of flight. The non-flying G. pennsylvanicus individuals have substantially reduced flight muscle masses and may be able to more efficiently allocate energy to other biological needs (flightless female field crickets, for example, tend to be more fertile than flying females).
All field crickets are able to make the universally recognizable cricket, “chirping” sounds. Males, though, are able to make the loudest and most noticeable sounds. The chirping is generated by the movement of “scrapers” found on the edge of the left forewing across a row of teeth-like structures located on the underside of the right forewing. The male field cricket generates a three note, highly trilled song which is answered by a more simplified, two note female song. The rate of chirping is directly influenced by temperature. Counting the number of chirps a male field cricket makes in 13 seconds, and then adding 40 to that number generates an approximate index of the environmental temperature (in degrees Fahrenheit).
Field crickets are omnivorous. They eat dried organic materials, fresh plant matter, small fruits, seeds, and, at extreme need, both living and dead insects. Plants such as crabgrass, ragweed, and chicory seem to be highly favored food sources. Large populations of G. pennsylvanicus can cause significant damage to agricultural crops, and when this species enters houses (typically in the late summer and early fall) wool, cotton, silk, nylon, rubber, and leather materials may be consumed. Population explosions in this species typical come after rainfall relieving prolonged drought conditions. The crickets feed at night and spend most of the daylight hours in warm, dark refugia. A field cricket must eat its body weight or more in food every day.
Predation, Disease and Parasites
Field crickets are preyed upon by a wide range of predators. Most bird species (including cardinals, turkeys, blackbirds, and even some hawks) will either preferentially or opportunistically eat field crickets. Red fox, box turtles, American toads, and many other mammalian, reptilian, and amphibian predators also vigorously consume field crickets. Field crickets are also subject to many diseases and parasites. There is a virus which causes body paralysis, fungal infections and protist colonizations of the intestines, ricketsia infections, mermithid worms (nematodes), and ectoparasitic mite infestations all of which beset these animals. There are also species of parasitic wasps which sting and paralyze field crickets and then lay their eggs in the still living cricket’s body. The larvae of these wasps feed upon the cricket as they grow and develop.
Mating and Reproduction
The male field cricket’s song is his proclamation of his readiness to mate. The males make energetic and highly conspicuous song displays, and those that sing the loudest tend to attract the most females. Those singing the loudest, though, also attract the most predators! There is, then, an extremely delicate balance between the biological success of a singing male cricket (i.e. successful reproduction) and his sudden termination by a hungry predator. This balance must have many subtle contributory factors which influence the ultimate fate of each individual. Consequences of "group singing” and the possibility of non-singing “lurkers” (phenomenon observed in studies of singing frogs and toads) are interesting areas for possible study in field cricket populations.
After mating, the females lay their eggs in moist sand or soil. The cerci of females are modified into digging ovipositors. Typically, eggs are laid in groups of fifty. A female will lay up to four hundred eggs. These eggs incubate in the soil for 15 to 25 days and then hatch into nymphs. These nymphs eat very vigorously and grow rapidly undergoing eight moults as they grow into the adult forms. These nymphs and the subsequent life stages up to adult all look fundamentally alike and differ only in their relative body sizes. This type of development is called “simple metamorphosis.” The adult stage is reached in about twelve weeks, but very few individuals actually reach this level: the average life span of a field cricket is only one week.
Field crickets are important agents in the decomposer communities of many ecosystems. They consume large quantities of often highly resistant, cellulose rich plant materials and produce fecal pellets that are easily decomposed by bacteria and fungi. Their activity, then, greatly accelerates the energy and nutrient flows in an ecosystem and provides plants with a much more abundant reservoir of highly available, essential growth factors. Field crickets also consume the seeds of many significant “weed” species thus reducing the potential of these rapidly growing, invasive plants to dominate both natural and human generated (i.e. lawns and gardens) ecosystems. Crabgrass in particular is a “weed” whose abundance can be reduced by the feeding activities of the field cricket. As mentioned above, though, when populations of the field cricket become excessively large, they can cause damage to agricultural crops. They can also do significant damage to clothing, furniture, rugs, and even rubber materials when they invade a house in large numbers.