Montana Field Guide

Preface to the Genus Oecanthus
The following is taken from Fulton (1915, June and October 1926), Walker (1962), and Funk (1982). Species in this genus are divided into 4 natural groups based on their morphology, color and habits. These groups are niveus, releyi, nigricornus, and varicornis. Only two groups occur in Montana, with 4 species in the nigricornus group and one species, the Snowy Tree Cricket (O. fultoni), in the releyi group.

Generally, tree crickets are characterized by their long, slender shape, pale colors and arboreal habits. The tegmina (forewings) of males are broad and flat, and female wings are long and narrow and wrapped closely to the body. Their legs are very slender, armed with two rows of minute teeth interspersed with a number of delicate spines. The tarsi (feet) are three-segmented with the second segment being small and compressed. The antennae are longer than the body, filiform and often ornamented with distinctive black markings. The first two basal antennal segments are distinctively marked with spots, which are a convenient diagnostic character for species identification (see illustrations for each species).

The Snowy Tree Cricket has an orange yellow spot on the top of the head between the eyes, and sometimes two similarly colored spots on the thorax. The body color and antennae are whitish to pale green (Fulton 1915, June and October 1926, Hebard 1928, Walker 1963, Helfer 1971, Capinera and Sechrist 1982, Vickery and Kevan 1985, Bland 2003, Capinera et al. 2004, Himmelman 2009, and Scott 2010).

Song production in Oecanthus
Song is produced only by males, which raise their forewings (tegmina) perpendicular to the body and vibrate them in a transverse direction, so that the overlapping inner portions rub against each other. The sound-producing mechanism is located near the base of the wings. It is a broad expanded distal area which serves as a resonator to increase sound volume. A short prominent transverse vein occurs beneath forming a rasp-like structure about 1-1.5 mm width with 20-50+ short teeth, depending upon species, inclined toward the opposite wing. The number of teeth is a diagnostic feature. The right wing, termed the file, bears a series of downward projecting teeth, overlaps the left, termed the scraper. When the tegmina are raised and alternately opened and closed, the song is produced only on the closing stroke. Due to this partial wing-motion cycle, cricket songs are constructed of sound pulses. If a cricket opens and closes its wings many time in succession, it produces a trill. If the wings are opened and closed a few times, pauses, and repeats the song again, it produces a chirp. Songs vary according to ambient temperatures and is distinctive by sound analysis between species.

The Snowy Tree Cricket sings mostly at night, beginning at dusk and continues until morning. Occasionally they will sing during the day on very cloudy or overcast days. This species will synchronize their chirps with neighboring males into a “chorus,” making locating an individual difficult. The song has been described as a series of loud, rich, evenly spaced chirps, the number depending on ambient temperature. The warmer the temperature the faster, and colder the slower. Thus, the Snowy Tree Cricket has been called the “The Thermometer Cricket,” the original species used by Amos Dolbear to create formulas for calculating temperature by counting cricket chirps. The formula for O. fultoni is: Tf = 50 + Number of chirps/minute – 92 ÷ 4.7. Simple method: Temp F = 40 + Number of chirps/13-15 seconds. For degrees Celsius, count number of chirps per 7 seconds + 5. (Compare with Field Crickets, Gryllus sp.) (Fulton 1915, June and October 1926, Himmelman 2009, Vickery and Kevan 1985, Walker 1969.

The Snowy Tree Cricket overwinters in the egg stage. Adults appear in late July or early August and can persist until the first autumn frost (Vickery and Kevan 1985, Himmelman 2009, and Scott 2010).

The following comes from Fulton (1915, June and October 1926), Hebard (1928), Walker (1963), Helfer (1971), Capinera and Sechrist (1982), Vickery and Kevan (1985), Bland (2003), Capinera et al. (2004), Himmelman 2009), and Scott (2010). The body length for males is 12 mm, and females 9 mm. Their ovipositor is 4 mm. The male stridulatory file is ±1-2 mm wide with a range of 38-45 teeth with an average of ±41. Males have tapering broad wings (tegmina) which are nearly half as wide as long at their widest point. The first antennal segment has a nearly circular black spot, and the second antennal segment possesses a black ovoid spot covering most of the segment.

All Oecanthus species are similar in general form, appearance and behavior as noted above. For over a century, in the older literature, this species has been named O. niveus, which is now the current name for the Narrow-winged Tree Cricket which does not occur in Montana.

Inhabits shrubs, vines, brambles (blackberry, raspberry, rose), low trees, orchard trees and sometimes the crowns of tall trees along woodland edges, fencerows, and home shrubbery (Bland 2003, and Himmelman 2009).

The food habits of all the Oecanthus species consist of a great variety of both plant and animal origin, but the food items must be soft enough to be masticated by their weak jaws. One of their dietary mainstays is aphids. They also consume plant material by chewing holes in leaves, outer tissue of stems, the anthers of some plant flowers, chew holes in ripe fruit (apples, peaches, plums, etc.) to feed on the inner pulp, and eat fruiting bodies of fungi (Fulton June 1926, Vickery and Kevan 1985, and Himmelman 2009).

Reproduction in Oecanthus
The following is taken from Fulton (1915, June 1926), Walker (1962), and Funk (1982). The mating and reproduction habits of all Oecanthus species are generally similar in behavior and complexity. When a female is attracted to a singing male, she approaches him from the rear because that is direction most of the sound travels and amplified by his wings. When the male senses the female’s approach, he stops singing, turns around and touches her with his antennae. It is thought that this “tasting” of her confirms she is the same species and an appropriate mate. The next step in the courtship ritual, (can vary slightly among species) the male again sings and rocks from side to side or pounds his abdomen on the substrate. If the female is receptive to his “romantic overtures,” she climbs onto his back, the male raises his tegmina at a 45° angle, and she begins feeding on a substance secreted from a glandular cavity, called the metanotal, metathoracic or Hancock’s gland (which he called the “alluring gland”) located between the wing bases. The secretions empty into a pit at the base of the male’s hind wings where they are accessible to the female once she is in the copulatory position. After she begins to feed, she allows the male to mate with her. During copulation, the male reaches his abdomen back, the female bends her abdomen downward connecting their genitalia, and the male passes a sperm-containing spermatophore to the female. The spermatophore is ovoid and possesses a thin, threadlike tube which enters the female, leaving the spermatophore to dangle outside her genital opening and, when internally attached, sperm begins to move through the tube. After copulation, the female always eats the spermatophore because it is thought to contain nutrients which may enhance egg production. The female remains astride the male for 5-20 minutes or more, continuing to feed from the metanotal gland. When she stops feeding, she dismounts, but the male may attempt to resume active courtship by repeatedly backing under the female until she either remounts or moves away. If remounting occurs, the renewed courtship may require another 20 minutes or more. Such resumed courtship and mating is thought to ensure that large numbers of sperm pass from his spermatophore into the female’s sperm-storage organ called the spermatheca. When the female is ready to lay eggs, sperm are released from the spermatheca and fertilize the eggs as they pass down the oviduct. The female selects a suitable egg-laying site on a woody or herbaceous plant to oviposit and chews a small hole in the stem, then moves forward slightly, arches her back, bringing her ovipositor perpendicular to the hole moving it up and down drilling the hole with thrusts and turning it around by twisting her abdomen. The drilling time may require 5-25 minutes, depending upon the plant’s wood or fiber density. Once the hole is drilled to the proper size and depth, the female moves an egg down her ovipositor, fills the hole with a mucilaginous substance, removes the ovipositor, and neatly caps the hole with chewed plant material. The entire process from chewing the bark to sealing the hole may take a quarter hour to nearly a full hour.

The Snowy Tree Cricket produces one generation per year and favors woody trees and shrubs for oviposition of its eggs, laying them in the soft inner bark. The wood is grooved by the female’s ovipositor, not drilled. In woody plants having a soft fleshy bark, branches measuring 1-3 inches in diameter are preferred. The eggs may be placed in any part of the bark, but the lenticels are favorite locations which are less resistant to the female’s grooving operations. In species having a hard bark, smaller diameter branches are selected, and eggs are often laid at the sides of buds. The number of eggs deposited by a female ranges from 24-75, with an average of 49. Upon hatching, the nymphs pass through 5 instars before reaching the adult stage (Fulton 1915, June and October 1926).