List of arthropods
Considering that the Dungeon is a dark, dank place filled with moist corners and rotting corpses, it's no surprise that it contains countless creepy-crawlies ranging in size from freakishly huge to terrifyingly gargantuan. Crawl's many arthropods are some of the weaker opponents you'll encounter, but they shouldn't be underestimated; a great many of them have poisonous bites or stings, more than a few also come with exotic and dangerous special abilities, and they tend to come in swarms. While there are some exceptions, vulnerability to poison is a common arthropod weakness. They lack internal skeletons, so Necromancers are unable to raise them as skeletons (they may still be zombified, however).
Arthropods in general are fairly common throughout the Dungeon and the Lair, but certain varieties are quite common in other areas. The Spider's Nest in particular is full of spiders (among other bugs).
B Worker ant - Poisonous critters that seek out puny adventurers to drag back to their nests.
B Soldier ant - The sort of giant ant that can chomp through armour and shake off stab wounds. Extra poisonous!
B Queen ant - Less nimble than other ants, but comes with a highly venomous bite and is always guarded by her numerous offspring.
t Fire crab - Scuttling pyromaniac menaces that turn the Dungeon into a furnace with their fiery breath.
y Killer bee - Painful alone and deadly in swarms, these pack hunters are a menace to the unprepared.
y Queen bee - Although extremely venomous, her lack of maneuverability makes her easier to deal with.
y Hornet - An oversized wasp dyed red in the blood of its paralyzed victims.
y Spark wasp - Electric swarming insects capable of launching themselves as bolts of living lightning.
y Vampire mosquito - Pesky undead insects that will happily suck the unwary dry.
Moths & Butterflies
b Butterfly - Harmless and pretty and occasionally in the way.
y Ghost moth - Invisible psychic predators with debilitating poisons.
s Redback - A notoriously venomous arachnid, capable of seriously poisoning even those who are resistant.
s Wolf spider - A powerful spider capable of tearing foes apart even without its venom.
B Giant cockroach - Common pests of the upper floors of the Dungeon, they're mostly harmless.
s Scorpion - One of the earliest opponents capable of seriously poisoning careless adventurers.
s Demonic crawler - Swift, hellish arthropods that partially resist most elements, including poison.
s Emperor scorpion - The beefiest arthropod of them all, they shrug off blows that would fell lesser bugs.
a Formicid - Rarely-seen humanoid ants who are most notable for their ability to burrow through solid rock.
B Death scarab - Undead swarming vermin that drain life and speed with their bites.
B Boring beetle - Beefy, but easily avoided. They tended to turn any floor with rock walls to swiss cheese if left to their own devices.
s Giant mite - Bloated, poisonous vermin found in the early Dungeon.
w Killer bee larva - Virtually zero threat, much like ant larvae.
s Spider - Scuttling poisonous pests. Individually weak, but they came in swarms.
s Trapdoor spider - Cowardly vermin that struck at those who walked past their hiding places and retreated underground when injured.
s Giant centipede - Although fragile, their poison stings could be hazardous.
B Boulder beetle - Tanks that normally lumbered along slowly, but they could suddenly start rolling at break-neck speed.
y Wasp - Although slower and more solitary than killer bees, their stings slowed and paralysed their victims.
0.19 - Added meliai and removed wasps and boulder beetles
0.18 - Added spark wasps, removed trapdoor spiders and plain spiders.
0.17 - Added entropy weavers, removed giant mites, boring beetles and goliath beetles.
0.16 - Added death scarabs, renamed yellow wasps and red wasps to wasps and hornets, respectively.
0.15 - Added ghost crabs, removed giant fireflies.
0.14 - Removed giant centipedes and moths of suppression.
0.13 - Added and quickly removed polymoths.
0.12 - Added moths of suppression and chaos butterflies, and removed bumblebees and ant larvae. Chaos butterflies were removed soon after due to flooding issues.