|scientific name Amphizoa |
Members of the three North American species are found in cool to cold freshwater streams. Adults and larvae live among stones or pieces of wood at the bottom.
No information available.
Broad-bodied and Tenebrionid in appearance, oblong, black to reddish-brown, 10-14mm long. Dorsal side of body pitted with coarse dots (puncate). Head is stout and broad, quadrate, and narrower than pronotum. Eyes are flat to slightly convex and project laterally slightly. Antennae are short, 11-segmented, and bare (filiform). First three antennal segments puncate; remaining segments bare and shiny. Mandibles are stout and blunt, concealed apically by large clypeus and labrum. Pronotum much narrower than elytra and is short and flat, and is basally sinuate, with anterior and posterior angles pointed and projected. The beetles are elongate-oval in silhouette, moderately convex dorsally. All body segments are piceous on dorsal surface. Notopleural sutures are clear. Tarsal formula is 5-5-5. All tibia with two short, terminal, almost equal spurs. Legs are slender and long, with no adaptations for swimming (not natatorial). Only mid-tibia with a row of setae in apical depression. Elytra are broad, subovoid and tapered to a blunt point apically; elytral surface is faintly punctulate, and striae are evident but faintly defined. Hindwings are fully-developed and the venation pattern includes oblongum and wedge cells. The abdomen has 6 visible sterna with the first sterna being broadly and completely divided by the hind coxae. First three abdominal sternites are fused. Sutures between all sternites are distinct. There is a visible but indistinct suture on the metathorax before the hind coxae. Abdomen is 8-segmented with weakly developed spiracles; only last abdominal tergite with normal spiracle pair. Hind coxae are large and occupy half the metathorax; inner lobes are contiguous. Epipleura is well developed and broad at the base, tapering towards the first sternite; narrow at the level of the other sternites and disappear near base of the anal sternite.
Holometabolous. Amphizoids lack structural adaptations for swimming, and are actually more efficient locomotors on land than in water. The beetles are unable to swim, and crawl on substrate at the bottom of streams. Larvae pupate out of the water on adjacent streambanks. Both adults and larvae are strict predators. Adult Amphizoids are able to carry out most life functions- feeding, locomotion, oviposition- as easily on land as in water. Under laboratory conditions, Amphizoid eggs and larvae thrive out of water, and even pupate normally. Larvae are of the caraboid type, and are elongated with flattened lateral lamellate projections, have two tarsal claws, and two short, spine-like cerci. Larvae breathe through the 8th abdominal segment. When disturbed, adults exude a yellowish fluid from the anus which has an odour described as that of cantaloupe melon or rotting wood. The function of this fluid is debated, but it is likely for predator-defense. Both adults and larve are frequently found attached to the roots of undercut vegetation at the stream edge, crawling along rocks and pebbles on the bottom of the stream, or found clinging to driftwood and other debris. When disturbed they can be seen floating on or near the water surface.
Larvae and adults are strict predators feeding on stonefly nymphs.
Among North American species, Amphizoa insolens is mainly found on the Pacific West-coast, with some extension into mountain ranges to the east. Amphizoa lecontei is restricted to the Rocky Mountain region; Amphizoa striata is restricted to western Oregon, western and central Washington state, and Vancouver Island, British Columbia. Ranges of A. insolens and A. striata overlap extensively.
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