297 

 Leech and Chandler: Coleoptera 



WILLIAMS, F. X. 



1936. Two water beetles that lay their eggs in the 

 frothy egg masses of a frog or tree toad. Pan-Pac. 

 Ent., 12:6-7. 



Key to Nearctic Families of Aquatic 



and Semiaquatic Coleoptera 



Adults 



1. First visible abdominal sternite completely divided 

 by hind coxal cavities (fig. 13:9), hind coxae im- 

 movably united to metathorax (if first 2 or 3 sternites 

 are hidden by expanded hind coxal plates (fig. 13:3a), 

 see family Haliplidae, following); first 3 visible ab- 

 dominal sternites connate, sutures partly obliterated 

 (less obviously so in Gyrinidae, which have a dorsal 

 and a ventral pair of eyes, and short, irregular anten- 

 nae) (fig. 13:23); antennae usually filiform or nearly 

 so. Suborder ADEPHAGA 2 



— First visible abdominal sternite extending for its 

 entire breadth posterior to hind coxal cavities, un- 

 divided (if both a dorsal and a ventral pair of eyes 

 present, see Gyrinidae in Adephaga, above); hind 

 coxae not immovably united to metathorax. Suborder 

 POLYPHAGA 9 



2. Hind coxae not contacting elytral epipleura (fig. 

 13: Id), separated from them by metasternal epimera 

 which contact 1st abdominal sternite as may the 

 metasternal episterna (except in Trachypachus of 

 Carabidae, but note the numerous setae, as long as 

 segments are wide, on its antennal segments); at 

 least some parts of body with erect individual setae; 

 typically terrestrial beetles (fig. 13:1c), with a few 

 species adapted to the intertidal zone of the sea 

 beach 3 



— Hind coxae contacting elytral epipleura and separating 

 metapleura from 1st abdominal sternite (see Trachy- 

 pachus, above); body often with vestiture, but without 

 individualized setae; aquatic beetles 4 



3. Scutellum present CARABIDAE 



— Scutellum absent (fig. 13:1c) OMOPHRONIDAE ■ 



4. Eyes divided by sides of head, appearing as 4: a 

 dorsal and a ventral pair (fig. 13:23); antennae short, 

 stout, 3rd enlarged and earlike, the following segments 

 more or less closely unified; middle and hind legs 

 greatly modified for swimming, short and flattened, 

 tarsi folding fanwise (fig. 13:226) GYRINIDAE 



— Eyes 2, antennae elongate, slender; hind legs suit- 

 able for crawling or definitely modified for swimming, 

 tarsi often flattened somewhat but never folding fan- 

 wise 5 



5. Hind coxae expanded into large plates, covering first 

 2 or 3 abdominal sternites and bases of hind femora 

 (fig. 13:36); legs hardly modified for swimming, hind 

 tarsi slightly flattened and fringed with long hairs 

 (which are usually closely applied to the tarsi in dry 

 specimens); small beetles, 5.5 mm. or less in length 

 (fig. 13:4a) HALIPLIDAE 



2 \l beetles actually found in water do not fit any of the choices 

 offered in the key, it is probable that they do not belong in this 

 habitat at all. Beetles commonly fly, fall, or are blown or knocked 

 into the water, and are washed in by rain. 



Many species live close to the water's edge, yet are not 

 truly aquatic. Without prior knowledge of the groups, it is not 

 always easy to recognize them as littoral rather than aquatic 

 species. The following keys to families (adults and larvae) 

 include the common shore dwellers, but only those which are 

 aquatic in some stage are treated in detail below the family 

 level. A partial exception is made for the few forms which occur 

 within the intertidal zone of the California sea shore (see Carabi- 

 dae, Ochthebius vandykei in Hydraenidae, Staphylinidae, Melyri- 

 dae, Eurystethidae, Throscinus crotchi in Limnichidae). 



— Hind coxae not expanded into largo plnte.s, not cover- 

 ing hind femora nor more than 1st abdominal Btornito 

 6 



6. Motasternum with a tran.svcr.se, triangular antocoxal 

 sclerite separated by a woll-markod suture (as in 

 fig. 13:3a); hind logs not adapted for swimming, 

 tarsi not flattened or (ringed with hairs but simple 

 and carabidliko; black or brownish beetles, 11 to 15.5 

 mm. long (fig. 13:1a) AMl'IIIZOIDAE 



— Metasternum without a transverse suture; no antecoxal 

 sclerite; hind legs modified for swimming, tarsi flat- 

 tened, usually fringed with long hairs (which arc 

 commonly stuck to tarsi in dry specimens) 7 



7. Middle of prosternum and its postcoxal process in 

 same plane (fig. 13:8a); front and middle pairs of 

 tarsi distinctly 5-segmented, segment 4 approximately 

 as long as 3; scutellum fully exposed, or concealed 



8 



— Middle of prosternum not in same plane as its process, 

 the latter bent (fig. 13:86); front and middle tarsi 

 4-segmented, or 5-segmented with 4th very small and 

 almost concealed between lobes of 3rd; scutellum 

 concealed (except in Celina spp.) (fig. 13:14.6). Sub- 

 family Hydroporinae of DYTISCIDAE 



8. Scutellum covered by bases of elytra and hind margin 

 of pronotum; hind tarsi with 2 slender curved claws 

 of equal length, tarsal segments nearly parallel -sided; 

 front tibiae (except in N otomicrus sp., a beetle 1.5 mm. 

 or less in length) with a curved spur or hook at apex 

 (fig. 13:18c) NOTERIDAE 



— Scutellum fully visible (fig. 13:16c); or if covered, 

 hind tarsi with a single straight claw, segments lobed 

 behind on outer side (fig. 13:9) 



(in part) DYTISCIDAE 



9. Tiny beetles, from about 0.5 to 1 mm. in length; hind 

 coxae usually laminate, tarsi 3-segmented; hind wings 

 fringed with long hairs 10 



— Beetles of various sizes, from nearly 1 mm. to 40 mm. 

 in length; at least hind tarsi with more than 3 seg- 

 ments; in very small dorsally glabrous forms, never 

 with hind coxae laminate 12 



10. Hind coxae widely separated; antennae 8-segmented, 

 short, compact, without long hairs (fig. 13:42e); staph- 

 ylinidlike beetles with truncate elytra and exposed 

 conical abdomen; aquatic species 



HYDROSCAPHIDAE 



— Hind coxae contiguous or almost so; antennae 11- 

 segmented; if elytra somewhat truncate and a few 

 abdominal segments exposed, note antennae; littoral 

 species 11 



11. Only 3 visible abdominal sternites; phalacrid-like 

 beetles, convex, polished, glabrous . . . . SPHAERHDAE 



— Abdomen with at least 5 visible abdominal sternites; 

 body form usually rather flattened, dorsally somewhat 

 to very hairy PTILIIDAE 



12. Antennae short, true segment 6 modified to form a 

 cupule (fig. 13:256), 7-11 (often reduced in number 

 to 3) forming a strong pubescent club, 1-5 (sometimes 

 reduced to 3 or 4) simple and glabrous; maxillary 

 palpi nearly always longer than antennae; head usually 

 with a Y-shaped impressed line on vertex 13 



— Antennae not so constructed, longer than maxillary 

 palpi; head without Y-shaped impressed line 15 



13. Antennal club of 5 pubescent segments; abdomen 

 with 6 or 7 visible sternites; transverse suture of 

 head not joined at middle by a posterior median suture; 

 tiny beetles, not more than 2.5 mm. in length (fig. 

 13:25e) HYDRAENIDAE 



— Antennae with only 3 pubescent segments beyond 

 cupule; 5 visible abdominal sternites, if a 6th is 

 present it is membranous (Hydrochus) or more or less 

 retracted under 5th (Berosus, Laccobius); transverse 

 suture of head, when present, directed angularly back- 

 ward at middle, meeting coronal suture to form a Y; 

 size varied, but species approaching 1 mm. in length 

 are convex and rounded 14 



