CPIE Project		Page A10
	Key to Aquatic Insects BEETLES  Order Coleoptera. When completed, the following key will cover both adult and immature stages. Adult aquatic beetles are air-breathing. The dytiscid pictured here is obtaining air through the posterior tip of its abdomen, which is seen just breaking the surface as the animal hangs head down in the water. The hind legs are adapted for swimming: more or less flattened and heavily fringed with hairs.

	131a	(104)	Antennae long and filiform (narrow, filament-like); maxillary palps short. In the water, frequently seen hanging head downward at the surface, or swimming by moving both hind legs together ~ Family DYTISCIDAE	[132]
	131b		Antennae short and club-shaped; maxillary palps as long or longer than the antennae. In the water air carried in a film on the ventral surface; swimming by moving hind legs alternately. Water scavenger beetles ~ Family HYDROPHILIDAE	[144]
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	132a	(131)	Adult beetle about 1 cm long or slightly more. Males (only) with as many as 30 sucker discs on the underside of fore and middle tarsi Rhantus pacificus Boisdduval
	132b		Adults smaller, less than 0.5 cm long and closer to 0.25 cm. Males with far fewer sucker discs on tarsi	[133]
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	144a	(131)	Underside of thorax having a sternal keel, projecting backwards as a long spine. Moderately large, 8-9.5 mmm long	[145]
	144b		Underside of thorax may have a sternal process, but this not a continuous keel terminating in backward-pointing spine; OR posterior segment only projecting as a short spine	[146]
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	145a	(144)	Pronotum and elytra uniformly black with a metalic hue Tropisternus salsamentus Fall
	145b		Pronotum and elytra metalic black with yellow lateral margins Tropisternus lateralis humeralis Motschulsky
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	146a	(144)	Larger species, typically greater than 7.5 mm long. Elytra with 10 regular series of tiny punctures	[147]
	146b		Smaller, less than 8 mm long. Elytra with only sutural stria posteriorly, otherwise without striae or lines of punctures	[148]
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	147a	(146)	Elytra with numerouis punctures forming distinct, well-defined striations (impressed lines). Endemic Limnoxenus nesiticus (Sharp)
	147b		Elytra punctures not forming distinct striae (lines) except along posterior edge of suture. Endemic Limnoxenus semicylindricus (Eschscholtz)
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	148a	(146)	Middle segment of thorax with a sharp keel along midline of underside. First segment of middle and posterior tarsi much shorter than second segment. { Color yellowish to yellowish brown with a black head and 3-4.1 mm long. Enochrus sayi Gundersen
	148b		Middle and posterior segments of thorax with convex processes. First segment of middle and posterior tarsi at least as long as second segment. { Color of elytra mostly black, except posterioor quarter yellowish red, 4-6.5 mm long.	[149]
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	149a	(148)	Elytra entirely black. Beetle 5.5-6.5 mm long. Indigenous(?) Coelostoma fabricii (Montrouzie)
	149b		Elytra black except at posterior end, which is yellowish red in color. Beetle 4.0-4.7 mm long. This species may not be established (Hansen, 1995) Coelostoma segne Balfour-Browne

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