Resin bugs: walking sticky traps

Resin bug (Reduviidae; Harpactorinae; Ectinoderini) with sticky forelegs
Resin bug (Reduviidae; Harpactorinae; Ectinoderini) with sticky forelegs

Reduvid bugs (Reduvioidea) – of which there are more than 7,000 named species – have evolved a diverse range of structural and behavioral adaptations to enable them to capture prey (4), including the application of sticky substances (“sticky traps”) to their forelegs by so-called resin bugs. Such ‘sticky trap predation’ is known from species in both the New and Old Worlds:

“Unique among known sticky trap predators, assassin bugs (Reduviidae) have evolved both exogenous and endogenous sticky trap predatory mechanisms: some trap their prey with sticky plant resins, some scavenge insects entrapped by sticky plant trichomes and others self-produce sticky secretions.” (Zhang et al., 2016) (3)

Resin bugs include the following tribes in the subfamily Harpactorinae: Apiomerini, Ectinoderini, and Diaspidiini (2). Resin bugs in the tribe Apiomerini (Reduviidae: Harpactorinae) are restricted to the New World and include species such as Apiomerus pilipes, which are natural enemy of stingless bees in Brazil (1). The Ectinoderini are restricted to the Oriental region and appear to be much less well-studied than their New World cousins. This tribe also includes species such as Amulius malayus, which dip their setae covered forelegs legs into tree resin and use it to trap stingless Trigona bees.
Resin bug (Reduviidae; Harpactorinae; Ectinoderini), Chiang Dao, Thailand

I came across some resin bugs on a ‘resin trap’ – a natural or human-induced outflow of resin at the base of a large dipterocarp resin tree – which I wrote about in a previous blog (5). Recently, I came across more of these amazing insects (see below) and thought it was worth including some additional photographs of them, to show their adaptations for capturing prey. The bugs cover themselves with plant resin, particularly the front legs, which helps them to capture prey, such as bees.

Resin bug (Reduviidae; Harpactorinae; Ectinoderini), Chiang Dao, Thailand

Some of the bugs have thick applications of resin on their fore-legs. Precisely what strategy they use to capture prey, sit and wait; wave their legs around; creep up on them (?), I am not sure of.

Resin bug (Reduviidae; Harpactorinae; Ectinoderini), Chiang Dao, Thailand. Showing forelegs covered with sticky, dark tree resin.

I came across one sitting in a hole in the resin trap (below) but they were generally fairly active, albeit moving somewhat slowly (as you might if covered with a sticky resin!).

Resin bug (Reduviidae; Harpactorinae; Ectinoderini) in a hole

The bees also collect resin for their nests and hover above the resin trap before landing on the sticky resin (below).

Stingless bees (Trigona sp.) hovering above the resin trap
Trigona stingless bees over resin

There were also lots of ants foraging for prey items on the tree and in the resin trap; probably Oecophylla smaragdina. Presumably they are clever enough to steer clear of the resin bugs, although I came across these two individuals quite close to each other.

Resin bug (Reduviidae; Harpactorinae; Ectinoderini) and ant (probably Oecophylla smaragdina).

I still do not have a firm identification of the resin bugs shown here, but they are probably a sub-species of Amulius malayus, or a closely-related species. The resin bugs must moult at some stage, and there was evidence of either cast skins (exuviae) or dead bugs within the resin (below).

Resin bug (Reduviidae; Harpactorinae; Ectinoderini) with cast skins or dead ones

There must be a lot to find out about these insects and they would make a fascinating study, although one would have to be careful of the ants’ nests which are found nearby. I quickly became covered with ants on one occasion when photographing the bugs!

  1. Silva, Alexandre Coletto da  and  Gil-Sntana, Hélcio R.. Predation of Apiomerus pilipes (Fabricius) (Hemiptera, Reduviidae, Harpactorinae, Apiomerini) over Meliponinae bees (Hymenoptera, Apidae), in the State of Amazonas, Brazil. Rev. Bras. Zool. [online]. 2004, vol.21, n.4 [cited  2017-11-29], pp.769-774
  2. Weirauch, C., Bérenger, J. M., Berniker, L., Forero, D., Forthman, M., Frankenberg, S., … & Marshall, S. A. (2014). An illustrated identification key to assassin bug subfamilies and tribes (Hemiptera: Reduviidae). Canadian Journal of Arthropod Identification26(2), 1-115.
  3. Zhang, J., Weirauch, C., Zhang, G., & Forero, D. (2016). Molecular phylogeny of Harpactorinae and Bactrodinae uncovers complex evolution of sticky trap predation in assassin bugs (Heteroptera: Reduviidae). Cladistics32(5), 538-554.
  4. Zhang, J., Gordon, E. R., Forthman, M., Hwang, W. S., Walden, K., Swanson, D. R., … & Weirauch, C. (2016). Evolution of the assassin’s arms: insights from a phylogeny of combined transcriptomic and ribosomal DNA data (Heteroptera: Reduvioidea). Scientific reports6, srep22177.


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