1. Introduction

Acanthaspis is a genus (Reduviidae: Reduviinae) of assassin bugs found in Africa and parts of Asia. The most recent large publication concerning the oriental species deals with species found in China. You can read more about the genus there.

Currently there are three Acanthaspis species known from Singapore on the Biodiversity of Singapore website: Acanthaspis inermis Stål, 1870, Acanthaspis nr. quadriannulata, and Acanthaspis signifera Stål, 1863. This species is not an Acanthaspis species, but most likely a female Psophis species. Here are some comments I have on the former two:

2. Acanthaspis inermis

A. inermis was described by Stål from the Philippines. Images of the type can be found here. Another image can be found on the Heteroptera Species Pages, which was collected from Zamboanga, Mindanao. With that in mind, here are some other iNaturalist observations I think may be A. inermis:
https://www.inaturalist.org/observations/209125303
https://www.inaturalist.org/observations/209127898
https://www.inaturalist.org/observations/115355948
https://www.inaturalist.org/observations/115555711

Besides the BoS website, more pictures of the “A. inermis” from Singapore can be found in iNaturalist:
https://www.inaturalist.org/observations/195675300
https://www.inaturalist.org/observations/101995084
https://www.inaturalist.org/observations/216458610
I’ve noticed some consistent differences between the Singaporean and Filipino individuals, which I attempt to illustrate by comparing observation 115555711 by hrc_habitat21 and 216458610 by moniquecordeiro. These include:

1. Scapus dark brown basal half + pale yellow apical half (S1) vs pale yellow throughout with small dark brown annulation(s) (P1)
2. Anterior pronotal lobe more or less uniformly dark brown (S2) vs with clear pale yellow elevated regions (P2)
3. Outer membrane cell without pale spot (S3) vs with a pale spot basally (P3)

These differences can also be observed in all the other links I posted. Acanthaspis species can vary in colour intraspecifically, some documented examples include Acanthaspis siva Distant, 1904 (posterior pronotum and legs), Acanthaspis cincticrus Stål, 1859 (mostly posterior pronotal lobe), and Acanthaspis quinquespinosa (Fabricius, 1781) (posterior pronotal lobe). Despite that, I still think these differences are enough to suggest the species in Singapore isn’t A. inermis, especially character 3.

The species from Singapore is more comparable to Acanthaspis laoensis Distant, 1919, although there are still come differences like A. laoensis having a uniformly black scape and also generally more colour on the anterior pronotal lobe (example).

3. Acanthaspis quadriannulata

This species from Singapore with four large round spots on the posterior pronotum, spinose humeral angles, and an elongate head is often labelled as A. quadriannulata:
https://www.inaturalist.org/observations/195669936
https://www.inaturalist.org/observations/203333735
https://www.inaturalist.org/observations/214311169

The characters I mentioned make it visually similar to Acanthaspis collaris Hsiao, 1976, which received an updated description in the Chinese Acanthaspis revision. On page 20 you can find remarks comparing it to A. quadriannulata and Acanthaspis flavovaria (Hahn, 1834). In particular I would like to highlight this statement:

A. collaris is also similar to A. flavovaria in body plan, however, it can be distinguished from the latter in each femur with two annulations and tibiae are bicolourous (vs. each femur with one annulation on subapical portion and tibiae are unicolourous in A. flavovaria).

The leg colouration (femora and tibia with two annulations) on A. collaris is similar to that of A. quadriannulata. The Singapore species, on the other hand, only has one subapical yellow annulation on the femora and unicolorous tibiae, making it much closer to A. flavovaria. Acanthaspis flavovaria was first described from Java, so the species identity may apply to these individuals, which look very much like the species from Singapore:
https://www.inaturalist.org/observations/131289359
https://www.inaturalist.org/observations/142052493

This post turned out to be a bit of a mess and much longer than I originally intended as I gradually unearthed more and more information about the bugs, I may return to clarify and elaborate more on certain things in the future, especially the bit on Toxocamptellus.

1. Introduction

Vesbius Stål, 1865 is a genus of relatively small Harpactorines (Reduviidae: Harpactorinae) distributed in the Indomalayan realm. One particular species, Vesbius purpureus (Thunberg, 1783), is widespread throughout the region. It often inhabits urban habitats, a trait which may have contributed to its range. The 15 Vesbius species that have been described more or less all have red bodies and mostly black heads and legs. This aposematic motif is adopted by some Harpactorines in other genera which inhabit the same region, causing many of them to have been misidentified as Vesbius on iNaturalist. This post seeks to clarify the generic position of these bugs, and also to act as a reference for my own future identifications.

2. TLDR - What is NOT Vesbius

A concise (although somewhat lacking) diagnosis of Vesbius can be found here provided by W. L. Distant. Notably:

Distinguished by the structure of the head, the postocular region being nearly three times longer than the anteocular area, the eyes are inserted near the apex of the head.

(shown in image below)

This head structure is not found in any of the other genera which may resemble Vesbius superficially. This characteristic can also be observed in nymphs.

3. Further elaboration on the non-Vesbius genera

More information for differentiating between the aforementioned species not belonging to Vesbius.

3.1 "Sphedanolestes"

In 1874, in an attempt to provide better taxonomic treatment for Sphedanolestes Stål, 1866, the entomologist Carl Stål assigned a number of subgenera to the growing genus. This consisted of:

1. Aulacosphodrus (later raised to genus) - Afrotropical species with long postocular regions
2. Graptosphodrus - New Guinea "Sphedanolestes"
3. Haemactus
4. Lissonyctus
5. Sphedanolestes - What I interpret Stål to have considered the "typical" Sphedanolestes, based on resemblance to the East Asian Sphedanolestes impressicollis Stål, 1866 (type of genus)
6. Sphactes

These classifications were discontinued and are not used today, but they still give us an idea into the species that superficially resemble Vesbius.

He keyed the subgenera here along with the Sphedanolestes species described at the time. The dichotomous key is presented in an unsual way by today's standards and is a little hard to follow, so I've converted it into this flow chart:

The species that resemble Vesbius, based on my interpretation, belong to what Stål considered Lissonyctes and Haemactus. Here is what Sphedanolestes politus (type of Lissonyctes) looks like: http://www2.nrm.se/en/het_nrm/p/sphedanolestes_politus.html . Its similarity to Vesbius purpureus is noted in its original description available here ("Vesbio purpureo haud dissimilis" → "Not unalike Vesbius purpureus"). This makes the subgenus a good fit for Harpactorines similar to the smaller of the two Sphedanolestes featured in the first image.

Stål used pronotum colouration to separate these two subgenera (along with others) from the "typical" Sphedanolestes (b, bb), and the angles of the posterior pronotal lobe to separate them from each other (i, ii). Interestingly, he notes that the first (visible) rostral segment of Haemactes widens posteriorly. This character, combined with the unusually robust body shape and S. trichrous being observed to be stenophagous on Crematogaster ants (pers. comms with @psophis_zelun), suggests that species described under this subgenus might not belong to Sphedanolestes at all.

3.2 Toxocamptellus

Toxocamptellus Breddin, 1900 is perhaps the most poorly documented genus featured in this post, and was first described by Breddin in 1900 here, with minimalistic drawing of the head and pronotum available here (Fig 11). Notably, it is the most robust of the bunch, and a characteristic to distinguish it from the other species/genera featured in this post would be to compare the length of the head and posterior pronotal lobe (length of head < length of posterior pronotal lobe).

Bonus: Toxocamptellus misidentified as Vesbius purpureus on flickr - https://www.flickr.com/photos/61827574@N03/49854803707