Sunday Spinelessness – The other monster

By David Winter 09/10/2011 6


I’ve never taken a good photo of an ant. I’ve tried plenty of times, but even when I’ve happened across queens, whose size should give the point’n’shooter the best chance to capture a passable shot, I’ve failed. I haven’t given up though, and that’s why I was spent about 15 minutes of this morning on my hands and knees pointing my camera at the little red, and slightly larger black, ants that patrol the paving stones in front of our house. I failed again, but if you spend 15 minutes contemplating the little creatures that run our world you are pretty much guaranteed to run into something interesting. Today I saw something I’ve never seen before

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A baby harvestman! I’ve written about harvestmen before, they are spider-relatives which are mainly scavengers rather than hunters and don’t have poison-delivering fangs. I don’t know if this one is a native or the introduced European harvestman (Phalangium opilio), but New Zealand has a surprisingly large number of native harvestmen (several hundred, and likely more awaiting description) and a suprisingly large number of those are truly weird looking. Arachnids like harvestmen and spiders have two sets of appendeges associated with their head. The chelicerae are use to grasp food and direct it towards their mouths whereas the pedipalps are strangely dual-purpose organs, used almost like an extra set of legs and also to deliver sperm during mating. Earlier this year I ran across a native Palpatores which amazingly giant chelicerae:

Today, while I was lining up the baby harvestman another misshapen harvestmen ran across the paving stones:

This one has considerably shorter legs than than the Palpatores, and when you zoom in on that mouth-gear you can see it’s the pedipals and not the chelicerae which are out-sized.

It’s not clear why the pedipalps are so spikey. They might help males to fight to fight off challangers and secure mates, but they probably also contribute to these creature’s excellent camouflage. The three forward spacing spikes on the carapace place this guy in the genus Aligidia. I took a few more photos before I let him go about his business:


6 Responses to “Sunday Spinelessness – The other monster”

  • Which part of New Zealand are you in, David? The top photo is not Phalangium opilio, though it could be another introduced species, Nelima doriae. Or it might be an adult of ‘Megalopsalis’ triascuta, a native New Zealand species that needs re-examination.

  • Hi Christopher,

    I’m in Dunedin. I’m afraid that’s the best shot of the smaller one that I managed to get, I don’t the others have any identifying features in better focus.

    I was actually going to email you about these. Both that Forster and Forster’s tip about the three spines placing the ‘big’ one in Aligidia was right and about what the small one might be.

  • Dunedin would rule out triascuta, which is a North Island species. I can’t really tell for certain from the photo, but on closer inspection I’m inclined to doubt an identification as Nelima doriae. It probably is a juvenile of one of the native harvestmen, and based on range I’m going to take a stab at Forsteropsalis marplesi (I don’t think that it’s a Pantopsalis). Forsteropsalis is the genus that includes most of the New Zealand species previously assigned to Megalopsalis. All the above is pretty shaky, though, because it is after all probably juvenile.

    Regarding the Algidia, I have to confess that my knowledge of Laniatores is pretty rudimentary. They haven’t been revised in New Zealand since Forster.

  • David, how can you tell that the harvestman shown in the top photo is a ‘baby’? Is it by size or are there other criteria that decided you?

    I live in the Pacific NW near Vancouver Canada & harvestman are abundant here as it’s on the edge of the rainforest. I’ve only seen 2 species around my house & never what I thought might be a juvenile so would love to learn more!

  • Hi Jude,

    I’ll admit that was a bit of a guess, and sadly only based on the size :). I spend more time that most people picking up logs and seeing what’s underneath and all the harvestmen I’ve ever seen are much bigger than this one. But as Chris (who revised the taxonomy of the New Zealand Palpatores so knows a thing or two abut this!) pointed out it could have been a fully grown member of a smaller species. If he is still following comments he might here he might be able to give you some pointers.

    BTW, I visited the Pacific NW last year and really loved my time in and around BC, quite similar to New Zealand in a lot of ways (and different in others).

  • From just external appearance alone, you probably can’t definitely ID juveniles unless you know the species in your area (the harvestman fauna of British Columbia was reviewed in 2009; you can find the paper at http://www.sfu.ca/biology/esbc/Journal/journal2009/Bragg_Holmberg_2009_Article_Galley.pdf). Not only will the juveniles be smaller, but they’ll also be less sclerotised and have reduced or lack ornamentation such as spines (if the adults have any).

    If you’re looking at a specimen under a microscope, it’s relatively easy to spot a juvenile. The genitalia will not be fully developed until maturity, and the genital operculum that covers the genitalia on the underside of the body will not be open at the front.