Aquatic Insects of Michigan

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

Nepidae - Water Scorpions

Introduction

Two genera are found in Michigan, 3 species of Ranatra and 1 species of Nepa. Principally lentic, Ranatra are commonly found in stills waters among overhanging plant vegetation and thin woody debris, but are also found in similar structures along streams, especially undercut banks. Nepa are most often found in shallow, muddy substrates of marshes or slow-moving streams in sections with little vegetation. This family has been thoroughly reviewed by Menke (1979) and Sites and Polhemus (1994).

Adults
(adapted from Menke 1979 and Sites and Polhemus 1994)

1a	a. Body enlongated and slender, nearly cylindrical in cross-section	Ranatra, 2
	b. Anterior lobe of pronotum not wider than head
	c. Abdominal sterna undivided
	d. Female subgenital plate laterally compressed, keel-like
1b	a. Body flattened, more oval in outline	Nepa apiculata Uhler
	b. Anterior lobe of pronotum wider than head
	c. Abdominal sterna divided longitudinally into median and parasternites
	d. Female subgenital plate broad, flattened
2a(1a)	a. Ant2 (second to most distal) with a lateral projection > 0.5x the length of Ant3 (most distal)	Ranatra fusca Palisot de Beauvois
	b. Stridulatory mechanism present on fore coxal cavity
2b	a. Ant2 (second to most distal) with lateral projection absent or < 0.5x the length of Ant3	3
	b. Stridulatory mechanism absent or present
3a(2b)	a. Profemur with width of distal portion 3x width of corresponding region of tibia	Ranatra kirkaldyi Torre Bueno
	b. Ant2 without a produced distolateral corner on either side, sometimes fused with Ant3
	c. Stridulatory mechanism absent
3b	a. Width of distal portion of profemur 2x width of corresponding region of tibia	Ranatra nigra Herrich-Schaeffer
	b. Ant2 with a produced distolateral corner, < 0.5x the length of Ant3
	c. Stridulatory mechanism (serrations, or sclerotized setae) present on fore coxal cavity

Nymphs (based on Menke 1979)

1a	a. Body enlongated and slender, stick-like in appearance, nearly cylindrical in cross-section
	b. Anterior lobe of pronotum not wider than head
1b	a. Body flattened, more oval in outline	Nepa apiculata Uhler
	b. Anterior lobe of pronotum wider than head

References

Sites RW, Polhemus JT. 1994. Nepidae (Hemiptera) of the United States and Canada. Annals of the Entomological Society of America 87(1):27-42.
Menke AS. 1979. Family Nepidae, pp. 70-75in Menke AS (editor), The semiaquatic and aquatic Hemiptera of California. Bulletin of the California Insect Survey 21:1-166 + xi.

Page created: July 16, 2003; Last edited: November 7, 2013 (EB)