Have

Necrosquito

Flying
Necrosquito enters with two oil counters on it.
Necrosquito gets +1/+1 for each oil counter on it.
Whenever another creature or artifact you control is put into a graveyard from the battlefield, put an oil counter on Necrosquito.

Atraxa's Skitterfang

Atraxa's Skitterfang enters with three oil counters on it.
At the beginning of combat on your turn, you may remove an oil counter from Atraxa's Skitterfang. When you do, target creature you control gains your choice of flying, vigilance, deathtouch, or lifelink until end of turn.

It of the Horrid Swarm

Emerge {6}{G} (You may cast this spell by sacrificing a creature and paying the emerge cost reduced by that creature's mana value.)
When you cast this spell, create two 1/1 green Insect creature tokens.

Nessian Hornbeetle

At the beginning of combat on your turn, if you control another creature with power 4 or greater, put a +1/+1 counter on this creature.

Masked Vandal

Changeling (This card is every creature type.)
When Masked Vandal enters, you may exile a creature card from your graveyard. If you do, exile target artifact or enchantment an opponent controls.

Giant Mantis

Reach (This creature can block creatures with flying.)

Skittering Heartstopper

{B}: Skittering Heartstopper gains deathtouch until end of turn.

Loam Larva

When Loam Larva enters, you may search your library for a basic land card, reveal it, then shuffle and put that card on top.

Adaptive Shimmerer

Flash
Adaptive Shimmerer enters with three +1/+1 counters on it.

Moldgraf Millipede

When Moldgraf Millipede enters, mill three cards, then put a +1/+1 counter on Moldgraf Millipede for each creature card in your graveyard. (To mill three cards, put the top three cards of your library into your graveyard.)

Symbiotic Beast

When Symbiotic Beast dies, create four 1/1 green Insect creature tokens.

Crawling Sensation

At the beginning of your upkeep, you may mill two cards. (You may put the top two cards of your library into your graveyard.)
Whenever one or more land cards are put into your graveyard from anywhere for the first time each turn, create a 1/1 green Insect creature token.

Devouring Swarm

Flying
Sacrifice a creature: Devouring Swarm gets +1/+1 until end of turn.

Durable Coilbug

{4}{B}: Return Durable Coilbug from your graveyard to your hand.

Pestilent Syphoner

Flying
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)

Dread Return

Return target creature card from your graveyard to the battlefield.
Flashback—Sacrifice three creatures. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Bilious Skulldweller

Deathtouch
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)

Grist, the Hunger Tide

As long as Grist, the Hunger Tide isn't on the battlefield, it's a 1/1 Insect creature in addition to its other types.
+1: Create a 1/1 black and green Insect creature token, then mill a card. If an Insect card was milled this way, put a loyalty counter on Grist and repeat this process.
−2: You may sacrifice a creature. When you do, destroy target creature or planeswalker.
−5: Each opponent loses life equal to the number of creature cards in your graveyard.

Fen Hauler

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)
Fen Hauler can't be blocked by artifact creatures.

Battlefly Swarm

Flying
{B}: Battlefly Swarm gains deathtouch until end of turn.

Kraul Swarm

Flying
{2}{B}, Discard a creature card: Return Kraul Swarm from your graveyard to your hand.

Conduit of Worlds

You may play lands from your graveyard.
{T}: Choose target nonland permanent card in your graveyard. If you haven't cast a spell this turn, you may cast that card. If you do, you can't cast additional spells this turn. Activate only as a sorcery.

Spinal Centipede

When Spinal Centipede dies, put a +1/+1 counter on target creature you control.

Giant Ankheg

Trample
Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
Other creatures you control have trample and ward {2}.

Getting

Hornet Queen

Flying, deathtouch
When Hornet Queen enters, create four 1/1 green Insect creature tokens with flying and deathtouch.

Prakhata Pillar-Bug

{B}: Prakhata Pillar-Bug gains lifelink until end of turn. (Damage dealt by this creature also causes you to gain that much life.)

Halo Scarab

{2}, Exile Halo Scarab from your graveyard: Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Don't Have

Scute Swarm

Landfall — Whenever a land you control enters, create a 1/1 green Insect creature token. If you control six or more lands, create a token that's a copy of Scute Swarm instead.

Giant Ladybug

Reach
When Giant Ladybug enters, you may search your library for a basic land card, reveal it, then shuffle and put that card on top.

Duskshell Crawler

When Duskshell Crawler enters, put a +1/+1 counter on target creature.
Each creature you control with a +1/+1 counter on it has trample. (It can deal excess combat damage to the player or planeswalker it's attacking.)