Maoristolus parvulus – extremely small and incredibly rare

These days I am going over my photo archives, doing some digital asset management. The work is mostly sorting images into folders and keywording, but make no mistake – it is a lot of work. Archive work is a great way to pass a cold winter, not that I’m complaining. We have been extremely spoiled this year with temperatures higher than the average for a Southern Ontario winter. And yet, winter is almost gone and I am past the midpoint of my archive workload, so my pace is good. What I like about this kind of work is that you discover many forgotten treasures; good photos that you left unedited for some time later, photos showing things you completely missed on first viewing, or even better, photos of extremely rare subjects. Today’s post is the latter case, a small detective story involving a strange bug named Maoristolus parvulus.

First, some background: in 2013 I went on a research trip to New Zealand. Even though my main work was studying ground weta, I took the opportunity to learn more about the native terrestrial invertebrates. One of the best finds were giant springtails of the genus Holacanthella, and I remember collecting a few of them together with their substrate for photographing later. The substrate itself, decomposing southern beech wood, was not sterile of course, and I found some small arthropods living in it (mostly ants and small centipedes). When I finished sorting through the wood particles I discovered what I thought was a small assassin bug nymph. I had no real interest in it, but it looked different from anything I know so I decided to take a few photographs before releasing it. After I returned home, I tried to identify it but I was unsuccessful. I decided to let it go and archived the photos. Little did I know, this was not an assassin bug

Aenictopecheid bug nymph (Maoristolus parvulus) from Fiordland National Park, New Zealand

Aenictopecheid bug nymph (Maoristolus parvulus) from Fiordland National Park, New Zealand

Stumbling upon these photos again, I decided to give identification another try. Like I said earlier, proper taxonomic identification can feel a lot like detective work, especially if you start from scratch and have no idea where to begin. There was no doubt that this was a bug. The piercing mouthparts, the antennae, the body structure – I have seen those before. But which family does it belong to? My initial gut feeling was assassin bugs (Reduviidae) because of the modified forelegs. This is where I deployed a key to the different assassin bug tribes and found absolutely nothing that looked even remotely similar. Frustrated, I tried looking for publications about NZ Heteroptera, checking sites like iNaturalist for similar observations, and even punching in different combinations of words on Google image search (yes, that’s something that even experienced entomologists do), hoping to get a lead. Eventually I landed on an old paper discussing NZ Enicocephalomorpha – a mysterious heteropteran infraorder containing two enigmatic families: Enicocephalidae and Aenictopecheidae.
The paper contained descriptions of several species, but what really caught my eye were the figures, clearly showing the same modified forelegs with short tarsi and strong claws! From here, all I had to do was to carefully follow this excellent lucid key, and get to the correct ID: Maoristolus parvulus.

Looking back, it seems that I wasn’t too far off. Infraorder Enicocephalomorpha, with its two families, was once treated as a sister group to the reduviid assassin bugs. Family Enicocephalidae, the larger of the two, contains about 400 species distributed worldwide. They are commonly called unique-headed bugs or gnat bugs, and there are fully winged as well as brachypterous (reduced wings) species.
Family Aenictopecheidae, however, is much more unique. It contains only 20 species in 10 genera worldwide, and these are some of the rarest bugs with several endemic species. They are so rare that they don’t even have a common name. It doesn’t help that they are also very small, Enicocephalomorpha bugs are generally between 3-5mm long. The bug I photographed was almost 3mm in length.

Aenictopecheid bug nymph (Maoristolus parvulus), extremely small and incredibly rare

Aenictopecheid bug nymph (Maoristolus parvulus), extremely small and incredibly rare

By the way, adult Maoristolus parvulus bugs have fully developed wings, so this is indeed a nymph. What else can I tell you about it? Not much. Enicocephalomorpha bugs and especially members of Aenictopecheidae are poorly known. We presume they are predaceous, hunting for small invertebrates in their habitat, such as springtails, mites, and worms.

Aenictopecheid bug nymph (Maoristolus parvulus) probing a piece of decomposing wood with its proboscis. We have no clue what these bugs feed on.

Aenictopecheid bug nymph (Maoristolus parvulus) probing a piece of decomposing wood with its proboscis. We have no clue what these bugs feed on.

These are, to the best of my knowledge, the only photos in existence of a live Maoristolus parvulus, and one of the only photos of a live aenictopecheid. As of now, there is only one other photo of a live aenictopecheid bug from Chile, a female Gamostolus subantarcticus with eggs. Sure, they are not the best photos, but when you see something this uncommon aesthetics take second place. Also keep in mind I had no idea what I was looking at back then. Thankfully today I am a little bit smarter.

3 thoughts on “Maoristolus parvulus – extremely small and incredibly rare

  1. I have been bitten by one of these bugs, and the experience was just as memorable to me as their distinctive morphology.

    It was at Barrington Tops, a rain forest world heritage area 4 hours north of Sydney, I was wandering on the track when one of these tiny winged adult landed on my left forearm, and almost instantly bit me (It’s strange, I know).

    The thumbing pain was almost unbearable for the next 10 to 15 minutes, although the affected area was limited, similar to a mosquito bite. The bite bought the bug just enough time to take off before I could collect it though.

    • You are talking about an assassin bug (Reduviidae), a different family and much more common. The bugs described in this post are not only extremely rare and cryptic in nature, but they are also tiny – only a few millimetres long. Their mouthparts cannot pierce the human skin, and they do not feed on blood.

  2. I am rather certain that the bug that bit me was not an assassin bug, and belongs to Enicocephalomorpha, likely Enicocephalidae. It is very small, around 3-4 mm long, active and winged. Had experience in a Hemiptera lab, and had seen many specimens of this group in late Cretaceous Burmese amber. Had also been bitten by a rather robust assassin bug years ago, and I learnt my lesson the hard way.

    I was also surprised that such a tiny bug could deliver a bite, seemingly unprovoked. A surreal experience for me.

    Members of Enicocephalomorpha are cryptic, but I suspect they are just overlooked soil organisms that are in fact rather numerous in the right habitat. Some species of Enicocephalidae have been documented swarming in large numbers, and I may just be lucky/unlucky enough to get in their way that day.

    Ordered a 2-5 x lens from Laowa a few days ago, and may also take pictures of these ting bugs later, if I could find one.


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