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The following key should enable the user to identify most specimens of Halobates and allied genera. The key generally works best for adult males, where the structures of the abdominal end usually provides good diagnostic characters. Adult females are usually much more difficult to identify. The terminology used in the keys is explained above.

1. Halobates and allied genera (tribe Halobatini)

*Dorsal surface of body with extensive pale markings on head, thorax, and abdominal dorsum (as Austrobates rivularis)*		Dorsal surface of body chiefly dark, pale markings usually limited to head and pronotum
Segment 8 of male (s8, t8) elongate, longer than wide, without spiracular processes; ventral styliform processes (st) short and stout, almost parallel	Segment 8 (s8) of male broad, wider than long, with spiracular processes; ventral styliform processes (st) long and slender, often diverging
Mangrove swamps South and East Asia	Freshwater streams Northeastern Australia	Various marine habitats Widespread
*Asclepios*	*Austrobates rivularis*	*Halobates*
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2. Asclepios

(under construction)

3. Halobates

Fore tarsal segment I, 0.3x or less longer than segment II Middle femur at most 1.05x longer than hind femur		Fore tarsal segment I, more than 0.3x longer than segment II Middle femur 1.1x or more longer than hind femur
Brown and yellow species usually with posterior margin of pronotum, most of thoracic pleura, and prominent stripes on femora, yellow	Dark brown to black species with most of thoracic pleura dark and only bases of anterior femora, yellow
Apices of male styliform processes slender and curved (as in Halobates mjobergi)	*Apices of male styliform processes slender and straight (H. zephyrus)*	*Apices of male styliform processes variable in shape (as in H. darwini)*
Northern Australia, New Guinea	Eastern Australia	Widespread
Halobates (Hilliella)	**Halobates (s.str.) zephyrus**	*Other Halobates* (s.str.)**
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4. Halobates, subgenus Hilliella

Fore femur of male depressed ventrally in distal fourth with an elongate patch of stiff hairs Male proctiger widest across middle; apices of styliform processes simple Length 3.3-3.8 mm (male), 3.4-4.2 mm (female)	Fore femur of male not modified ventrally, more or less tapering in width toward apex Male proctiger widest in basal third Slightly larger species, length 3.6-4.5 mm (male), 4.3-4.7 mm (female)
	Male proctiger distinctly produced laterally in basal third; apices of styliform processes slightly widened, pointed Thorax and abdomen above chiefly dark brown	Male proctiger widened but not distinctly produced laterally in basal third; apices of styliform processes simple Thorax and abdomen above chiefly brown or yellowish brown
Female meso-metanotum without dark bristles	Female meso-metanotum without dark bristles	Female meso-metanotum with scattered, long dark bristles
Northern Australia, New Guinea	Northern Territory, Western Australia	Western Australia
**Halobates (Hilliella) mjobergi**	**Halobates (Hilliella) lannae**	**Halobates (Hilliella) robinsoni**

5. Halobates, subgenus Halobates

*Yellow marks on dorsal head surface limited to a pair of oval marks at the base (as in Halobates germanus)* Interocular width of head subequal to or more than 3.6x width of an eye	Yellow marks on dorsal head surface more extensive, either with a crescent-shaped mark at base (as in Halobates hayanus) or with prominent yellow stripes along eyes (as in H. zephyrus) Interocular width of head less than 3.6x width of an eye
Body including thoracic and abdominal venter, uniformly dark	Conspicuous yellow or brown markings on some parts of venter
On ocean surface	In various coastal marine habitats
*Oceanic Halobates* (s.str.) species**	*Coastal Halobates* (s.str.) species**
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6. Oceanic Halobates (s.str.) species

Large species, 4.0 mm or more (females) or 4.4 mm or more (males)	Small species, less than 3.8 mm (females) or less than 4.0 mm (males)
	Antennal segment I much more than 0.5x as long as segment IV Fore tarsal segment I about 0.6x longer than segment II Male abdominal end as illustrated	Antennal segment I 0.5x as long as segment IV Fore tarsal segment I about 0.4x longer than segment II Male abdominal end as illustrated
All oceans	Indian and Pacific Oceans	Pacific Ocean
Halobates (s.str.) micans group	**Halobates (s.str.) germanus**	**Halobates (s.str.) sericeus**
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7. Halobates (s.str.) micans group

Hind femur long, more than 0.8x as long as middle femur and at least twice as long as hind tibia	Hind femur short, less than 0.8x as long as middle femur and not twice as long as hind tibia
Male proctiger relatively short and broad, finger-like produced laterally	Male proctiger as broad as long, laterally produced but not finger-like
	Fore tarsal segment I subequal to or slightly longer than segment II Left styliform process of male bowed outward, not right angled	Fore tarsal segment I shorter than segment II Left styliform process of male bent abruptly upwards at a right angle
Eastern Pacific Ocean	Eastern Pacific Ocean	All oceans
*Halobates (s.str.) sobrinus*	*Halobates (s.str.) splendens*	*Halobates (s.str.) micans*

8. Coastal Halobates (s.str.) species

Fore tarsal segment I subequal to or longer than segment II Large species, length 5.8 mm or more		Fore tarsal segment I shorter than segment II Small species, length less than 5.8 mm
Male abdominal segment 8 enclosed within the enlarged, tubular segment 8 Right styliform process very short and deformed	Male abdominal segment 8 clearly visible, never enclosed within a tubular segment 8 Right styliform process may be short, but not deformed
Western Pacific Ocean	Indo-Pacific
Halobates (s.str.) fijiensis group	*Large Halobates* (s.str.) species**	*Small Halobates* (s.str.) species**
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9. Halobates (s.str.) fijiensis group

Male proctiger almost parallel-sided	Male proctiger more or less shield-shaped, sides not parallel
Female connexiva forming two large triangles No black bristles on anterior margin of meso-metanotum	Female connexiva not modified No black bristles on anterior margin of meso-metanotum	Female connexiva not modified Stout black bristles present on anterior margin of meso-metanotum
	Right styliform process of male decurved at apex, reflexed at base and visible from above Female very broad posteriorly, width of body through hind coxae wider than head through eyes	Right styliform process of male flattened, its apex lanceolate, not visible from above Female only as broad through hind coxae as width of head through eyes
Tonga	New Caledonia, Vanuatu	Fiji
**Halobates (s.str.) salotae**	**Halobates (s.str.) katherinae**	**Halobates (s.str.) fijiensis**

10. Large Halobates (s.str.) species

Right styliform process of male segment 8 much shorter than left process and directed outward	Right styliform process of male segment 8 similar to left process, not directed outward
	Male proctiger broadly expanded laterally, with sub-parallel sides	Male proctiger at most narrowly expanded laterally, usually protruding but never parallel-sided
Micronesia	Indo-Pacific
**Halobates (s.str.) mariannarum**	Halobates (s.str.) kelleni, princeps, etc.	Other large Halobates (s.str.) species
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11. Halobates (s.str.) kelleni, princeps, etc.

Male fore femur with a tubercle beneath. A large species, over 6 mm	Male fore femur not modified. Smaller species, length not over 5.8 mm
Male proctiger with two pointed prominences on each side	Male proctiger with one pointed prominence on each side	Male proctiger with postero-lateral angles rounded
Indo-Australian		Andaman Sea, India
**Halobates (s.str.) princeps**	Halobates (s.str.) kelleni, and alluaudi group	**Halobates (s.str.) elephanta**
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12. Halobates (s.str.) kelleni and alluaudi group

Proctiger much longer than broad, anterolateral angles angulate. Length 4.5 mm (male)	Proctiger about as broad as long, anterolateral angles rounded. Length 5.0-5.8 mm (male)
	Apices of male styliform processes tapering in width	Apices of male styliform processes blunt
Female thorax in side view strongly arched		Female thorax not modified
Samoa	East Africa, Madagascar, Seychelles	Mauritius
**Halobates (s.str.) kelleni**	**Halobates (s.str.) alluaudi**	**Halobates (s.str.) tethys**

13. Halobates (s.str.) matsumurai group

Smaller species, length of male less than 6 mm	Larger species, length of male 6 mm or more
	Male body oval, much wider at the bases of legs than at anterior margin of meso-notum	Male body cylindrical, parallel-sided, hardly, if at all, wider at the bases of middle and hind legs than at anterior margin of meso-notum
Palau Is., New Guinea	China, Japan, Korea, Taiwan	Indo-Australian
**Halobates (s.str.) nereis**	**Halobates (s.str.) matsumurai**	**Halobates (s.str.) browni, esakii**

14. Halobates (s.str.) formidabilis, etc.

Fore femur of male strongly incrassate, fore tibia with a long spinous process on inner margin Male pronotum distinctly swollen Inner margin of fore tibia of female sinuate	Fore femur and tibia of male not modified Male pronotum not distinctly swollen Inner margin of fore tibia of female straight
	Fore tarsal segment I, 0.6x or less length of segment II	Fore tarsal segment I, more than 0.6x length of segment II
Andaman Sea, India, Sri Lanka	Indo-Pacific
**Halobates (s.str.) formidabilis**	Halobates (s.str.) proavus group	*Other Halobates* (s.str.) species**
	Go to 15	Go to 23

15. Halobates (s.str.) proavus group

Male proctiger subtriangular Fore tarsal segment I, 0.3x (male) or 0.4x (female) as long as segment II		Male proctiger more or less pentagonate Fore tarsal segment I, more than 0.3x (male) or 0.4x (female) as long as segment II
Males with black bristles along sides of meso-metanotum Male styliform processes slender	Males without black bristles along sides of meso-metanotum Male styliform processes stoter, left one strongly curved
Female thorax with a mid-dorsal, longitudinal groove and an orange stripe	Female thorax without groove and orange stripe
Indo-Malayan		Indo-Pacific
**Halobates (s.str.) proavus**	**Halobates (s.str.) maculatus**	*Other small Halobates* (s.str.) species**
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16. Other small Halobates (s.str.) species

Apices of styliform processes of male boot-shaped	Apices of styliform processes of male variable in shape, but never boot-shaped
	Both male and female completely yellow beneath	Male not completely yellow beneath, thoracic venter darkened
Indo-Australian	Australian	Indo-Pacific
Halobates (s.str.) sexualis group	**Halobates (s.str.) regalis, whiteleggei**	*Other small Halobates* (s.str.) species**
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17. Halobates (s.str.) sexualis group

Male and female meso-metanotum with scattered dark bristles	Male and female meso-metanotum without dark bristles
*Male proctiger almost symmetrical; lateral, right-hand finger-like projection not much longer than the left-hand projection (as in Halobates peronis* and H. acherontis)**		Male proctiger strongly asymmetrical; lateral, finger-like projections on right side very long
Indo-Australian	Australia, Southern New Guinea	Australia, Southern New Guinea
Halobates (s.str.) **dianae, murphyi, peronis, sexualis**	**Halobates (s.str.) acherontis, darwini**	**Halobates (s.str.) herringi**
Go to 18	Go to 19

18. Halobates (s.str.) murphyi, peronis, sexualis

Apices of styliform processes almost symmetrical, only slightly widened	Apices of styliform processes asymmetrical, distinctly widened
	A small species, length 3.9 mm (males and females)	A large species, length 4.5 mm (males), 4.6 mm (females)
West Malaysia, Sri Lanka	Bismarck Arch., Philippines, Solomon Is.	Northern New Guinea
**Halobates (s.str.) sexualis**	**Halobates (s.str.) dianae, peronis**	**Halobates (s.str.) murphyi**

19. Halobates (s.str.) acherontis, darwini

Body length 4.5-4.8 mm (male) or 4.3-4.8 mm (female)	Body length 3.8-4.2 mm (male) or 3.8-3.9 mm (female)
Meso-metanotum with few short dark bristles	Meso-metanotum with numerous long dark bristles
In mangroves Australia, Southern New Guinea	In rivers Western Australia
**Halobates (s.str.) darwini**	**Halobates (s.str.) acherontis**

20. Halobates (s.str.) regalis, whiteleggei

Fore tarsal segment I, 0.5x (male) or 0.6x (female) length of segment II. Male terminalia as illustrated	Fore tarsal segment I, 0.4x (male) or 0.5x (female) length of segment II. Male terminalia as illustrated
Hind coxae of female shorter, only about 2.0x as long as wide	Hind coxae of female very long, about 3.0x times as long as wide
Australian	Eastern Australian
**Halobates (s.str.) regalis**	**Halobates(s.str.) whiteleggei**

21. Halobates (s.str.) hayanus group, etc.

Male and female with scattered black bristles on meso-metanotum. Male terminalia as illustrated	Male and female without scattered black bristles on meso-metanotum
	Male proctiger with a distinct patch of black spine-like bristles on each side. Styliform processes almost symmetrical, their apices diverging	Male proctiger without a patch of black spine-like bristles or only a group of small spines. Styliform processes neither symmetrical nor diverging apically
	Female more than 4.3 mm	Female 4.3 mm or smaller
Galapagos Is.	Indo-Australian	Indo-Pacific
**Halobates (s.str.) robustus**	**Halobates (s.str.) calyptus, hayanus**	Halobates (s.str.) bryani, and poseidon group
		Go to 22

22. Halobates (s.str.) bryani and poseidon group

Left styliform process of male visible from above, both processes diverging posteriorly Female without black bristles on hind acetabula	Left styliform process of male not visible from above, both processes converging posteriorly Female with a group of stout black bristles on hind acetabula
A small brown species, 3.3-3.5 mm	Yellow colouration of head usually crescent-shaped, never reaching bases of antennae, occasionally with a yellow spot at bases of antennae	Yellow colouration of head extensive, extending uninterrupted to bases of antennae, leaving a lyre- or arrow-shaped spot in center
Fiji Is.	East Africa, Madagascar	Red Sea
**Halobates (s.str.) bryani**	**Halobates (s.str.) poseidon**	**Halobates(s.str.) melleus**

23. Other Halobates (s.str.) species

Left styliform process curved outward and visible from above		Left styliform process not curved outward and visible from above
Female with yellow colouration of venter limited to abdominal segments and sometimes middle acetabula		Female with yellow colouration of venter more extensive, usually extending forward to bases of fore legs
Malayan	Indo-Pacific	Indo-Australian
**Halobates (s.str.) trynae**	Halobates(s.str.) flaviventris group	Halobates (s.str.) panope and japonicus group
	Go to 24	Go to 25

24. Halobates (s.str.) flaviventris group

No dense, stiff black bristles on hind acetabula Undersurface of middle acetabula with a wide yellow band Male terminalia as illustrated	Dense, stiff black bristles on hind acetabula Undersurface of middle acetabula without a wide yellow band Male terminalia as illustrated
Hind coxae of female short and straight, never 1.5x as long as fore tarsal segment I	Hind coxae of female elongate and curved, at least 1.5x as long as fore tarsal segment I
Indo-Pacific	Central Pacific
**Halobates (s.str.) flaviventris**	**Halobates (s.str.) hawaiiensis**

25. Halobates (s.str.) panope and japonicus group

Right styliform process of male curved outward and visible from above; lateral edges of male proctiger rounded Female with median triangular area on meso-metasternum, entire abdominal venter, and basal third of fore femora, yellow	Right styliform process of male neither curved outward nor visible from above; lateral edges of male proctiger angular Yellow colouration of female venter more limited, basal parts of fore femora dark
	A large species, 5.0-5.2 mm in length Male terminalia as illustrated Female without black bristles on meso-metanotum	A small species, much less than 5.0 mm in length Male terminalia as illustrated Female usually with black bristles on meso-metanotum
India, Sri Lanka	Japan	New Caledonia
**Halobates (s.str.) galatea**	**Halobates (s.str.) japonicus**	**Halobates (s.str.) panope**

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Last update: 04 september 2002