Odontomachus haematodus with parasite. Armenia, Belize.
I can’t imagine what an insect infected with a mermithid nematode must feel. In Belize last week we encountered several parasitized trap-jaw ants, each stumbling about with a belly twice the heft of that in a healthy ant. Scaled to human size, a mermithid would be at least as intrusive as an anaconda coiled among the intestines.
Young worms infect ant larvae via contaminated soil in the brood nest. Adult ants who developed with a parasite sapping their nutrients eclose in a recognizably stunted fashion: a swollen, worm-hosting abdomen and a curiously shrunken head. I was surprised on photographing the victims that the trap-jaw could still snap shut audibly and convincingly.
How affected are mermithized ants? Compare an infected individual to a healthy one (albeit of a different species):
Top: a mermithid-carrying Odontomachus haematodus ant with distorted abdomen and shrunken head; bottom: a healthy Odontomachus clarus worker showing typical proportions for an uninfected ant.
When mature, worms break free from their hosts. The process kills the poor ant, but it frees the nematode to mate and lay eggs.
Still. One more reason I’m glad not to be an insect.
Canon MP-E 65mm 1-5x macro lens on a Canon EOS 7D
ISO 200, f/13, 1/100 sec
diffused overhead twin flash
This is creepy:
An x-ray image of an old Myrmica sulcinodis specimen reveals a coiled monster within. (Image: Sándor Csosz)
Among the odder ant-attacking parasites are mermithid worms. These nematodes sit coiled inside their hosts’ abdomens, consuming stored reserves and disrupting normal development. Infected ants have smaller heads and a distended gaster, a distortion striking enough that taxonomists failing to recognize the signs of parasitism have occasionally described these forms as novel species.
The online early edition of Myrmecological News carries a new report by Sándor Csosz where the author x-rays suspicious specimens in the genus Myrmica where parasitism may have duped early myrmecologists. Indeed, images of two purported “species” reveal the worms in all their glory.
I won’t be too quick to criticize other taxonomists’ mis-steps, however. I’ve made the same error myself. I once collected what I thought was a trimorphic Pheidole in Paraguay, giving them a temporary species number and their own tray in my collection, discovering only years later that the odd “intercaste” was actually parasitized majors of the common Pheidole flavens.
source: Csosz, S. 2012. Nematode infection as significant source of unjustified taxonomic descriptions in ants (Hymenoptera: Formicidae). Myrmecol. News 17: 27-31 Online Earlier.