Ooth orientation

PhilinYuma · Sep 10, 2009

My apologies to whoever noted that their females had laid ooths with the same orientation in the last couple of days; I can't find your post. I was reminded of this when reading a PDF article on Orthodera novaezealandia, in New Zealand Entomologist 26:3 26:3 (2003) "Fifty percent of the oothecae faced within 15° of true north on open sunny branches and tree trunks." (Thanks, Superfreak). I have noticed a similar conformity among local S. limbata ooths, usually laid more or less parallel to the ground on walls running east-west. In fact I have found none on walls running north-south. Has anyone else noted this conformity of ooth orientation?

Rick · Sep 10, 2009

I have not Phil. One was laid in my yard last night and it was north/south or up and down. I find them all ways. Stagmomantis often laid on buildings when I was growing up in the midwest but they were in all directions. I do find that chinese tend to lay their ooths close to other ooths. I have no idea why though.

Christian · Sep 10, 2009

This certainly has to do with some microclimatic conditions. Depending on wind direction, insolition etc. the ooths are placed as optimal as possible: temperate species tend to use sunny rocks or walls if they deposit near the ground or on branches (as in Iris, Mantis, Orthodera, Empusa, Stagmomantis): rainforest species usually avoid water, so they lay on the unterside of leaves (Deroplatys, Hymenopus) or in crevices (Deroplatys, Macromusonia). Some avoid heat by large foamy masses (Idolomantis, Gongylus), or lacking/excessive humidity by producing an airy layer (Hoplocorypha, Liturgusa).

The aggregations are interesting, three theories were discussed more or less intensively:

1. Microclimatic conditions are so optimal that females choose the same place coincidentally.

2. Predator/parasitoid avoidance by clustering.

3. Competition between females.