Do Millipedes/ insects have the ability to shrink?

[Bugoodle]

We have a flat backed millipede(either Polydesmus angustus or Polydesmus serrratus). We've had him for about 5 months and we don't know whats going on for about a month now. He looks like he's been changing size back and forth new dark shades. A few weeks back he bit and sprayed my niece. Today me and my niece noticed that he's gotten smaller in size or at least shorter. Is this normal or is someone replacing millipedes? lol It's quite a mystery but my niece is becoming frustrated over it. It's bugging us both. I have noticed that he's been remaining burrowed for the past couple of days. He's usually in the water dish or curled around a quencher gel. We just got some spring tails and he likes the dirt that they came. I just hope the springtails aren't causing any problems.

Thanks!

 

[kevink]

Arthropods don't have the ability to shrink at will, I suppose some might seem to become smaller if they were hibernating, but I think 

it would be virtually imperceptible.

Maybe there are more millipedes in your container than you think-

Someone replacing the millipedes... reminds me of some tv shows I've seen about non-owners taking "care" of animals or plants while the owner 

is away, and replacing the dead ones. 

 

[Bugoodle]

No, there's only one flat-back. Me and my niece keeps track on our bugs because she's always playing with them. They all have names too. lol  In her main tank, she owns one flat-backed millipede, one scarlet millipede, 6 roaches(1 large  deathhead nymph, 2 halloween hissers, 2 madagascar hissers, and 1 mimic beetle roach), 2 rice scarabs, 1 sugarcane beetle, 1 rainbow dung beetle, 1 rainbow darkling beetle, 1 domestic cricket, 1 eastern tent moth caterpillar, and a random snail. In a tiny tank she also owns a picnic beetle and a confused flour beetle she raised from a mealworm.

We also have rearing cages for 3 baby domino roaches, 2 chrome roaches, and 2 wild unidentified roaches.

All I have is a harlequin flower beetle, a rainbow dung beetle, and a juvenile N. American giant millipede. lol 

We have lots of bugs and possibly more. Her birthday is coming and she really wants a bess beetle. Oh god, the only thing she needs is a 20 gallon tank!