Montana Field Guide

The following comes from Severin (1935), Alexander and Bigelow (1960), Helfer (1971), Capinera and Sechrist (1982), Vickery and Kevan (1985), Capinera (2001), Bland (2003), Capinera et al. (2004), Elliot and Hershberger (2007), Himmelman (2009), Scott (2010), and Weissman and Gray (2019). Both the Spring Field Cricket and Fall Field Cricket (Gryllus pennsylvanicus) are basically indistinguishable in morphology, color, song and were once thought to be the same species, Gryllus assimilis (as reported by Hebard (1928) and Severin (1935)). Also, the older genus name Acheta will be used in some literature prior to 1960. When field studies revealed that they are two separate species due to their evolutionary development barrier known as “allochronic,” a mode of speciation of species living, growing, or reproducing at different times of the year (see Phenology below). These two barrel-shaped species are shiny black or dark brown with no markings. Their heads are slightly wider than their bodies and the wings (tegmina), and can be either black or light brown. Females are distinguished from males by their long, spear-like ovipositors which are split at the tip.

Calling song stridulation: The song of both species is described as “a series of clear, loud chirps given at a rate of about one to four per second depending upon ambient temperature.” They sing both day and night. There is little, if any, detectable difference in their stridulation. Sound is produced by raising the wings and rubbing them together, which draws the wings' teeth of scrapers and files, the sound-making mechanism, across each other. Their auditory receptors (ears) are located at the knee on the tibia of the front legs. Through recorded sonograms, researchers have recognized 6 functional songs in the reproductive behavior of these species: (1) The Calling Song, (2) The Courtship Song, (3) The Aggression Sound, (4) The Courtship Interruption Sound, (5) The Post-copulatory Sound, and (6) The Recognition Sound. Refer to Alexander (1966), Huber and Thorson (1985), Alexander and Meral (1967), Walker and Carlysle (1975), and Masaki et al. (1987) for the details of cricket acoustical communication.

Calculating temperature F: (#1) Tf=50 + Number of chirps/minute – 40 ÷ 4. Or use a simpler formula:(#2) Tf=4 + Number of chirps/15 seconds. Crickets generally do not sing at temperatures below 55 degrees F or above 100 degrees F. The original (#1) formula was published by Alfred Dolbear (1897), Tufts College, and became known as “Dolbear’s Law.”

The following is taken from Alexander and Bigelow (1960), Capinera (2001), Capinera and Sechrist (1982), Capinera et al. (2004), Elliot and Hershberger (2007), Himmelman (2009), Scott (2010), Vickery and Kevan (1985), and Weissman and Gray (2019). The Spring Field Cricket overwinters (diapause) as mid-sized nymphs. They mature quickly and adults begin singing and mating in late spring (April to May) continuing on into early July, when they die. The Fall Field Cricket (Gryllus pennsylvanicus) overwinters (diapause) in the egg stage and adults begin singing in late July or early August and continue on into the fall or the first killing frost. Where these two species overlap in occurrence and habitat, there is usually a period of silence in mid-summer (July) when no cricket songs are heard since G. veletis is dying out and G. pennsylvanicus is maturing. These differences in overwintering diapause and adult singing occurrence have been recognized by researchers for decades past when these species were considered races of G. assimilis.

The following comes from Bland (2003), Helfer (1971), Capinera and Sechrist (1982), Vickery and Kevan (1985), Capinera (2001), Bland (2003), Capinera et al. (2004), Elliot and Hershberger (2007), Himmelman (2009), Scott (2010) and Weissman and Gray (2019). Adult body length for both species, males and females, can range from 13 mm to 34 mm. The field crickets are highly variable in their morphology and there are many papers in the literature focused on the subject. Body size tends to vary with latitudinal distribution of individuals, with smaller crickets occurring in the more northern areas. The female ovipositor is often slightly longer in G. pennsylvanicus than G. veletis.

Could be confused with the Ground Crickets, Allonemobius spp., and the House Cricket, Acheta domesticus which is an Old-World species imported into North America in the 1700’s via shipping. It can now be found throughout the continent since it is commonly reared on “cricket farms” and sold in pet shops for food, bait shops and in laboratories for biological research. Escaped feral populations occur across the eastern and central states (except Florida) and southern California. To date, no feral House Crickets have been recorded in the field for the western half of the country nor in Montana (Capinera et al. 2004).

The Spring Field Cricket favors ground debris, rock piles, under shrubs and in burrows. It tends to be more solitary, sedentary, aggressive, and burrow-inhabiting and is rarely as numerous as the The Fall Field Cricket (Bland 2003, Capinera et al. 2004, and Vickery and Kevan 1985).

These crickets’ diets are varied and considered omnivorous, consuming leafy plant matter, roots, flowers, fruits, and seeds. They also eat dead insects and are reported to be cannibalistic. Sometimes these crickets’ nymphs and adults exhibit predatory behavior, consuming grasshopper eggs, pupa of flies and caterpillars, flea beetles, and insects from spider webs. They also invade homes and are documented to gnaw on such products as fur, wool, linen, cotton and paper products. They are generally not considered a serious pest unless they are abundant, and this usually occurs with the Fall Field Cricket (Gryllus pennsylvanicus), which is more gregarious, abundant and widely distributed than the Spring Field Cricket, G. veletis (Bland 2003, Capinera 2001, and Severin 1935).

These species have one generation per year and pass through 8-9 nymphal instars before reaching the adult stage. Adults generally live for 8 to 10 weeks. Eggs are laid in firm, damp soil about 0.8 inches below the surface. The eggs are about 3 mm long, cylindrical, slightly bent with rounded ends and light yellow or cream colored. The color changes and the shape enlarges as the embryo develops. A female may lay a range of 150-400 eggs, deposited singly, but several may be in close proximate clusters. Except for the overwinter eggs of Gryllus pennsylvanicus, the eggs hatch in about two weeks. Upon hatching, in both species, the nymphs pass through 8 to 9 instars before reaching the adult stage (Bland 2003, Capinera 2001, and Severin 1935).