In Holmes, the poison of giant centipedes is “in many cases … weak and not fatal.” Mechanically this is a +4 bonus to saving throws. It’s still save-or-die. In Moldvay, failing the saving throw causes an illness lasting for 10 days, reducing movement to ½ rate, and prohibiting other physical activity. Thus the poison of the Holmes centipede is less likely to take effect (+4 to saving throw) but has much more dire consequences (death). Also according to Holmes, giant centipedes “come in many colors (gray, black, red-brown, etc.)." Perhaps each has a different type of poison.
Black giant centipedes: +4 bonus to saving throw, failed saved causes sickness as per Moldvay
Grey: Moldvay type
Red-brown: Holmes type
Red-orange: save-or-die, as Holmes, no bonus to the saving throw
To the typical dungeon denizens, and experienced adventurers, these differences would be well-known, but neophyte adventurers might be unaware of them.
MINI-MODULE. Caverns of the Crawlers
Here is a pdf of this.
Wandering Monsters. Check once per 10 minutes. 1 in 12 chance.
1. 2-5 orcs
2. 1-4 orcs and Leutenant Oriker from H
3. 1-4 orcs and Shaman Grak from H
4. 1 giant fly
5. 1 giant ant
6. 1-4 giant centipedes
A. Ladder up to 10’ wide ledge where the cave entrance is located. The entrance is only 3’ high (once 50’ into the cave, the height rises to about 10 feet) and so entry and exit is not too easy. Roll 1d6 and subtract 2 for the number of orc guards present here at any given time. Allow the possibility of zero guards. There always should be guards here, but discipline is lax. Wisps of smoke waft from the cave mouth, noxious and very weird smelling, this smoke is present near the ceilings throughout the caverns (comes from Grak's poison making operation at H).
B. Well concealed wire (2 in 6 chance of detection) triggering falling rocks (dexterity check to avoid 1-12 damage).
C. On northern wall, an ancient skeleton in shiny chain mail (cursed -1). The pit is 20’ deep but full of water 2-5’ deep, resulting in less damage from the fall, but there is a pit viper in the water.
D. 2’ wide, 40’ deep pit. Orcs put refuse, etc. down these, that is all.
E. Water, 2-5’ deep. 1 in 6 chance of slipping if moving through here without caution.
F. Water, 4-11’ deep. A shiny statue at the bottom of pool. It is a worthless painted statue the orcs tossed into the water. There is a giant leech in the pool.
G. 2-8 orcs
H. Grak’s workshop. Here the orc shaman Grak (crafty, eccentric, brooding, forgetful, cruel, 3 HD, cure light wounds (x2), dispel magic) is attempting to create a poison usable on weapons from the deadly venom of the red-orange giant centipedes. Also present is orc lieutenant Oriker (hot-headed, a drunk, weak leader, 2 HD) who has no faith in Grak’s scheme. In addition, another 2-7 orcs are here, and their gear (sleeping pallets, weapons, the usual equipment, etc). Pots full of vile smelling liquids simmer over a small fire in south-east corner (Grak's operation, this is where the strange smelling smoke comes from), crude alchemical equipment around the fire. There is a giant centipede cage for on the east wall, with 1-4 of the red-orange variety in it. (Grak and the orcs might have treasure as you deem fitting oh DM).
I. Slave pen. 3-18 human/demi-human slaves locked in fenced in southern portion. Sick and weak. They are forced by the orcs to plumb the depths of the giant centipede infested tunnels at K, in search of the red-orange variety. Obviously this is dangerous work. Grak promises freedom to any slave who can bring him two of the rare red-orange giant centipedes. No one individual has yet captured two and so no one knows if Grak will keep his word.
J. Top of the Cliff. 3 orcs with crossbows and flasks of oil, torches on walls. Ladder down to K. The guards are here to both to keep centipedes from climbing up the cliff and to force the slaves go into the centipede infested tunnels (K), instead of cowering at the base of the cliff.
K. Giant centipede infested tunnels. Ladder up the cliff to J. Narrow maze-like tunnels penetrate far into the mountain and are teeming with the critters. If PCs venture into these tunnels, or are forced to, there is a 1 in 10 chance each minute of encountering 1-4 giant centipedes (determine type randomly).
L. Tomb. The orcs shun this place. The entire cave radiates magic; using detect magic will not register anything particular, other than this general presence of magic. There is a sarcophagus on the northern wall, a table with a dagger on it in the center of the cavern, and a scroll on a small stand near the west wall. There is a loose stone (1 in 6 chance of detecting per 10 minutes searching) in north-west corner, and under the stone is an iron box with a bottle of red ink and a brush. If any chaotic being touches the scroll case, then all chaotics in the cave take 1-8 damage, save vs. magic for half. If any chaotic touches the iron box, then all chaotics in the cave suffer 3-18 damage, save vs. magic for half. The scroll depicts a dagger in a circle. If the party uses the brush and ink to paint a circle around the dagger on the table, then the sarcophagus may be safely opened with no ill effects. There is a 2000 gp crown in the sarcophagus. If the circle has not been drawn when the sarcophagus is opened, then poison gas is triggered from the sarcophagus and the dagger animates and attacks as a 4th level fighter (AC 3, hp n/a). It is not possible to “kill” the dagger, a successful hit will knock the dagger away for a moment, prohibiting the dagger's attacking during the next round. If the party leaves the cave then after 1-6 hours, the dagger will resume its position on the table. Any lawful being that spends more than 10 minutes in this cave will heal 1-6 points damage (don’t tell them, they’ll be pleasantly surprised later), once per day.