Why are newly hatched houseflies weak?

[Wonderpants]

I’ve just ordered what’s just my second batch of housefly pupae. They seem to be gradually hatching if taken out of the fridge for a while, and I can then put the hatched flies into the terrarium for the mantis to catch. However, this batch are all coming out only able to crawl around, and some are even ending up partly attached to the pupa after hatching or even unable to emerge in a couple of cases. I’m not sure if it’s a dodgy batch, if they’ve gotten too cold, or should be fed before being put into the terrarium to give them some energy. Any thoughts?

 

[Mantid-Tim]

That happens when they get old. They dry out I think is what contributes. They should always be above 30-40% humidity or else the pupa will dry out. Spray a little water and mix around every week or so.

 

[Wonderpants]

Thanks!