I enjoy the concept but I have concerns about the execution. I did my best to feed all three of your race variants through the Detect Balance Guide to try to estimate how balanced these are compared to each other and also to other races. Unfortunately, I did have to do a little guess work on a couple of traits because they are not clearly represented elsewhere.

Agile scored a 23, Flying scored a 20, and Burrowing scored a 28. The average PHP and EE race falls at about 25 points and I would say a good homebrew race should probably hit between 24 and 27. So based on that scale there is a little balance work to do but not too much. There are some other concerns though.

Flying races are just naturally problematic. If at all possible it's best to avoid them but if you aren't concerned about the issues they can cause, then it's not the worst thing. I'd actually recommend if you keep it that you up it to a standard 30 ft fly speed. The flyers need a slight boost anyway and if walking everywhere is faster I don't see as much use of the flying speed.

A bigger concern overall I think is the static +1 Armor Class that they all get and burrowing gets twice. That stacks on top of whatever armor they are wearing. There is potential to be OP and its honestly not very thematic either. I think you better get the idea of a carapace by giving them a natural armor of 13+Dex when not wearing other armor. This is much less strong but is more flavor appropriate. Heavy armor wearing races won't benefit from it but that's because they are wearing better armor, while casting classes basically get mage armor AC without having to cast it. 

I would personally try something like:

Ability Score Modifier: +1 Str, +1 Dex [Score:8]
Carapace: Natural Armor 13+Dex. [Score: 3]
Size: Medium [Score: 0]
Languages: Common, 3 others, choice of 1. [Score: 2]
Variants: Agile, Flying,  Burrowing

Agile
Ability Score Modifier: +1 Dex [Score: 4]
Walking Speed: 40ft. [Score: 5]
Advantage: Dex Saving Throws [Score:4]
Total Score: 26

Flyer
Flying Speed: 30ft. [Score: 16]
Total Score: 29

Burrower
Burrowing Speed: 30 ft. [Score: 12]
Darkvision: 60ft. [Score: 3]
Total Score: 28

A bit more evenly balanced and I think less problematic. But that's just my two cents. Feel free to disregard.

Hey, thanks! That's all super helpful. I  really appreciate it.

I haven't looked back at this race in a while. When I have some time I'll assess this and work some things out.

I could tell there was a thematic problem with the flying, lol. I just gave them darkvision as a bonus because I felt flying wasn't exciting enough. Honestly I agree that it makes more sense for the burrowing.

Again, thank you for the assistance!

You could probably just have a rule against them wearing heavy armor due to their anatomy 

Quote from Hoddmimir >>

A bigger concern overall I think is the static +1 Armor Class that they all get and burrowing gets twice. That stacks on top of whatever armor they are wearing. There is potential to be OP and its honestly not very thematic either. I think you better get the idea of a carapace by giving them a natural armor of 13+Dex when not wearing other armor.

 I personally disagree here. This may be powerful at low levels with few save based threats, but most DMs can adapt enemies if necessary. It definitely loses a bit of its potency above very low levels where there are less saving throw based threats. You could do something like advantage on Con saves and/or tremorsense while fully burrowed underground (or just permanently). That would make a fun build primarily for warlocks where you put down an aoe control spell with concentration and stick your head out to force enemies back into it with Eldritch Blast when you sense them leave the area. 

I really like this species and it also feels organic and unique.