We’re covering the springtail officially known as Entomobrya assuta Folsom, 1924 as this week’s North Carolina “Insect” of the Week. That’s right! They’re not true insects but rather six-legged critters classified in a more inclusive lineage called Hexapoda. Despite this taxonomic situation I think this species is still worthy of receiving such a high honor.

This springtail species was described by Justice W. Folsom in 1924, based on observations of specimens collected under the bark of trees in Vermont and New York. According to the taxonomic treatment syntype specimens were sent to both the NY State Museum in Albany and the American Museum of Natural History, though the Illinois Natural History Survey has nine syntypes as well. At least one synonym is known: E. maizeae Wray, 1948.

Like all Entomobryidae, E. assuta has the following characteristics: prothorax reduced, scales present, 4th abdominal segment longer than the 3rd, trochanteral organ (i.e., a patch of short, differentiated setae on the trochanter) present, furcula well-developed, color pattern diagnostic. The ventral surface of head also has several diagnostic characters. As with other species classified in Entomobrya the mucro (at the apex of the furculum) is bidentate with basal spine, dental spines are absent, the antennal bulb is well-developed, and the unguis (tarsal claw) has 1 outer tooth, 2 lateral teeth, and 4 inner teeth. What separates assuta from other Entomobrya, though is the pigmentation (variable pattern, but usually with an irregular tranverse band across posterior margin of the 2nd and the whole of the 3rd abdominal segment, with posterior 1/4 of body dark except 2-5 pale spots) and the chaetotaxy (the arrangement of scales on the body).

Very little is known about the natural history of Entomobrya assuta. They probably sustain themselves on fungi, like most springtails (Hopkin 1997).

Though the original specimens were found under the bark of various trees, including apple, this species can also be found in bird nests, mushrooms, bee nests, rodent nests, leaf litter, and just about any other habitat where their micro-sized food can be found (typically pollen, algae, fungal spores etc.; see Castaño-Meneses et al. 2004). One study (Graves et al. 1977) explored springtails, including E. assuta, in the context of shelf fungi communities in western North Carolina.

There are currently no records in GBIF and no comprehensive list of specimens available. Christiansen and Bellinger (1980) report that specimens are known from Arizona east to Florida and north to Iowa, Wisconsin, and Quebec. The NCSU Insect Collection has 10 slide-mounted specimens, from all over the USA – including one from a motel room in Fargo, ND and one from California.

• Folsom, J. W. 1924. New species of Collembola from New York State. American Museum novitates; no. 108: 12 pp. http://hdl.handle.net/2246/4492
• K. Christiansen and P. Bellinger. 1980. The Collembola of North America, north of the Rio Grande: A taxonomic analysis. Grinnell College (Grinnell, Iowa) 1322 pp.
• Castaño-Meneses et al. 2004. Feeding habits of Collembola and their ecological niche. Anales del Instituto de Biología, Universidad Nacional Autónoma de México,Serie Zoología 75(1): 135-142. 2004 link
• Currently there are no records available for this species in GBIF: http://data.gbif.org/species/13829636/
• Entomobrya assuta Folsom, 1924 species page at BugGuide: http://bugguide.net/node/view/85733
• Graves, R. C., Graves, A. C. F., Wray, D. L. 1977. Collembola associated with shelf fungi (Polyporaceae, etc.) and some other microcommunities in the highlands area of western North Carolina. Annals of the Entomological Society of America 70 (6): 890-892. link [note: a large portion of the Wray Collembola collection is archived at NCSU]
• Hopkin, S. P. Biology of Springtails (Insecta: Collembola). Oxford University Press, USA. 344 pp.