Aquatic Insects of Michigan

by Ethan Bright, Museum of Zoology Insect Division and School of Natural Resources and Environment
University of Michigan

Brachycentridae (Humpless Case-makers, Log-cabin Case-makers, American grammon) of Michigan - Identification

Introduction

There are two genera found in Michigan, Brachycentrus Curtis (5+1 species) and Micrasema McLachlan (2 species).

Taxonomic references: Flint 1984, Ross 1944, Wiggins 1996

Adults (adapted from Flint (1984) and Ross (1944)

1a	Males (Determined by male genatalia)	2
1b	Females	not distinguishable
2a(1a)	R1 of front wing with a kink at level of chord (sinuate at base of stigmal region)	Brachycentrus Curtis, 3
	also: Maxillary palpus of male 3-segmented, spurs generally 2,3,3, rarely 2,2,3 or 2,2,2
2b	R1 of front wing straight or only slightly sinuate to the margin	Micrasema McLachlan, 8
	also: Forewing with R4+5 forked distincly beyond s
3a(2a)	Cerci completely fused dorsomedially	Brachycentrus americanus (Banks)
	also: Clasper with a large, lobate, mesal process from near apex in lateral aspect; tenth tergum with a bifid structure just above tergites
3b	Cerci divided dorsomesally although they may be touching basally	4
4a(3b)	Tenth tergum with 1 macrochaetae apically (rarely a small second one may be present on one side)	Brachycentrus numerosus (Say)
	also: Apical portion of clasper distinctly elongate and slender, being at least twice as long as broad
4b	Tenth tergum lacking macrochaetae	5
5a(4b)	No distinct sclerotized area between base of tenth tergum and cerci, and area lacking brush of short setae (hirsute lobe)	Brachycentrus occidentalis Banks
	also: Apex of clasper strongly angled and mesally produced, tip at most slightly notched
5b	Distinct sclerotized area between base of tenth tergum and cerci present, which also bears a brush of short setae	6
6a(5b)	Tenth tergum distinctly divided apicomesally	Brachycentrus fuliginosus Walker
6b	Tenth tergum only barely emarginate apicomesally	7
7a(6b)	a. Apex of clasper in lateral aspect rounded	Brachycentrus lateralis (Say)
	b. Tenth tergum in lateral aspect with tip rounded
7b	a. Apex of clasper in lateral aspect tapering to a point	Brachycentrus incanus Hagen
	b. Tenth tergum with tip distinctly angled dorsad
8a(1b)	a. Dorsobasal lobes of tenth tergite very thin and elongate, length at least 5x its width in dorsal view	Micrasema wataga Ross
	b. Posterior arms of tenth tergite spatulate, broadened apically and with rather straight mesal margins
8b	a. Dorsobasal lobes broad, length less than 5x its width in dorsal view	Micrasema rusticum (Hagen)
	b. Posterior arms not as above
	also: Ninth segment narrow but complete dorsally and with ventral sclerotized straps or thickenings

Pupae (from Ross 1944)

1a	Hook plates of fifth and sixth segments with fewer, larger hooks	Brachycentrus
1b	Hook plates of fifth and sixth segments with more, smaller hooks	Micrasema

Larvae (note: larvae of Brachycentrus fuliginosus is unknown)

1a	a. Middle and hind legs long, femora approximately same length as head capsule	Brachycentrus, 2
	b. Ventral margin of femora, tibiae and tarsi of mid- and hindlegs bearing a row of modified short, spinous setae
	c. Tibiae produced distally into a prominent process, from which stout spurs arise
1b	a. Ventral margins of middle and hind legs shorter, femora much shorter than head capsule	Micrasema, 6
	b. Ventral margin of femora, tibiae and tarsi of mid- and hindlegs without a specialized setal fringe
	c. Tibiae not produced distally into a prominent process, althouth spurs arise from about the same point on unmodified tibiae
2a(1a)	Venter of first abdominal segment with 1 pair of submesal setae	Brachycentrus americanus (Banks)
	also: carina on the gena just mesad of the eye short
2b	Venter of first abdominal segment with 2 pair of submesal setae	3
3a(2b)	Mid- and hind-tibiae with 1 large basomesal setae	4
3b	Mid- and hind-tibiae with a row of 3-5 basomesal setae	5
4a(3a)	Head brown, with indistinctly paler muscle scars	Brachycentrus occidentalis Banks
4b	Head contrastingly marked with brown stripes on a yellow background	Brachycentrus lateralis (Say)
	also: mid- and hindtibiae and tarsi pale with a narrow, fuscous dorsal stripe
5a(3b)	Head with 5 distinct longitudinal, fuscous bands, often with mesal band touching inner bands of genae near apex of frontoclypeus	Brachycentrus incanus Hagen
5b	Head with mesal band broadly confluent with inner bands of genae for apical third of frontoclypeus, thus head appears to bear 4 elongate pale spots	Brachycentrus numerosus (Say)
	also: frontoclypeus with a cluster of pale muscle scars near apex; mid- and hind-femora generally pale with fuscous dorsal and ventral margins
6a(1b)	a. Case made of sand, curved	Micrasema rusticum (Hagen)
	b. Head pale yellow to light brown, with bold, regular muscle scar pattern
	also: Frontoclypeus lacking four circular muscle scars and dark semicircular markings at the constriction of the frontoclypeus; setae 2 and 3 on anterior margin of frontoclypeus not appreciably thicker than other head setae
6b	a. Case largely vegetable matter, straight	Micrasema wataga Ross
	b. Head lacking pattern of bold, regular muscle scars
	also: head pattern with a very irregular or mottled appearance

References

Chapin JW. 1978. Systematics of Nearctic Micrasema (Trichoptera: Brachycentridae). Ph.D. Dissertation, Clemson University, South Carolina. 136 + xiv.
Flint OS. 1984. The genus Brachycentrus in North America, with a proposed phylogeny of the genera of Brachycentridae (Trichoptera). Smithsonian Contributions to Zoology 398:1-58, iv.
Ross HH. 1944. The Caddis Flies, or Trichoptera, of Illinois. Bulletin of the Illinois Natural History Survey 23(1):1-326.
Wiggins GB. 1996. Larvae of the North American caddisfly genera (Trichoptera). University of Toronto Press: Toronto, Ontario. 457 pp. + xiii.

Page last edited: May 21, 2016 (EB)