It is not surprising, therefore, that swarms made the cover of several pulp-era adventure magazines. But what if you want to use some of these covers as the basis for an encounter or two in your adventure? The core rulebook offers statstics for four types of swarm: mundane bats, vampiric bats, insects, and rats. It does not, sadly, offer a swarm-specific Critical Hit table. If the judge uses Table M (Monsters) for critical hit effects, the results are often absurd within the context of the encounter. We will rectify that here.
Every swarm in the core rulebook also has a special effect if it hits, requiring a saving throw to avoid it. In the case of rats and bats, this is the potential for disease. In the case of insect swarms, this is a venomous sting that can deliver additional damage. For some reason, bats carry more interesting/diverse diseases than rats, but you can easily change that in your own adventures!
So far so good. Now, let's add a few swarm types from pulp-era magazine covers! If some of these seem silly to you, well, you are not alone.
Crab swarms are far more dangerous to slow characters or those who have been disabled due to injury. They attack with claws and bite, and shred flesh from opponents who do not dislodge them quickly enough. Some crabs also have a 20' climb speed.
Crab swarms occur in real life, although not usually as dramatically as they do in pulp fiction. There is some evidence that aviator Amelia Earhart, having sustained injuries in a crash landing, was eaten by giant coconut crabs. The most effective use of crab swarms I have encountered was in Allan Quatermain by H. Rider Haggard. I attempted to reproduce the effect in an encounter in Stars in the Darkness. Clark Ashton Smith's The Master of the Crabs is another inspirational source.
This is a bit of silliness, but it might make a good encounter in a forest of evil repute. Flying squirrel are not normally dangerous. Even the few reported "attacks" seem pretty tame. But for some reason the squirrels in the image are large, and out during the daylight, and apparently have a taste for meat. Do with it what you will.
10% of lizard swarms carry a venomous bite, requiring a DC 5 Fort save to avoid 1 point of temporary Stamina damage (heals normally).
Lizard swarms are common enough in role-playing games, Individual lizards can and do bite humans, and some of them may have bites that are painful, or even dangerous, but you are extremely unlikely to ever encounter lizards attacking en masse in real life.
As a side note, I would prefer to have the images for each swarm alternate between the left side of the text and the right, but cover illustrators (or those who purchased these images in the pulp era) seem to prefer images that face right. They also preferred to tempt their presumed audience with a torn blouse or two.
Monkey bites are unfortunately not at all uncommon. Monkeys can carry diseases such as tetanus and rabies. The judge is recommended to use the disease table for bats in the core rulebook. You could even pump up the risk, considering the virulence of some monkey bites, but if you do this you should make sure that the players have some way of knowing that monkey bites are dangerous.
An arboreal monkey swarm can also fling feces, sticks, overripe fruit, and the like at targets prior to melee attacks. These attacks allow the swarm to target all creatures in a 30' x 30' square, which must make Will saves (DC 5 +1 per additional round) to avoid fleeing the area. Of course, the monkeys can move faster than most targets, so fleeing is seldom effective. A monkey swarm can use this tactic to drive targets toward preferred attack sites, or away from their territory.
This doesn't have to be just piranha; this can be any relatively small but dangerous fish the judge desires. Are there swarms of freshwater eels? If the judge wants them, there are! Obviously, the easiest way to avoid these dangers is to not get into the water in the first place. Once you are attacked, the easiest way to survive is to get out of the water.
Water protects piranha swarms from fire-based magic and similar effects, granting a +2d shift on the dice chain to saving throws and reducing any damage suffered to one-quarter. The judge may rule that the medium allows electricity-based spells to affect all targets in range (including any potential PCs), and cold-based spells to affect all targets in half normal range, so long as they are at least partly in the water.
When characters are successfully attacked by the swarming bite of piranha, they must succeed in a Luck check, or the piranha attack in a frenzy that round, doing an additional 1d5 damage to all targets that failed their Luck check. For creatures without Luck scores, assume a base score of 10. Particularly cruel judges may have "exploding" frenzy damage. Each time a "5" is rolled, add an additional 1d5 damage. In this way, cattle - and adventurers! - may be stripped to the bone in seconds.
Crack open the core rulebook and pick your favorite snake venom from Appendix P. If the serpent you want isn't there, you will find a few additional options in 50 Fantastic Functions For The D50...less than half of them are serpent venoms, though, because the article details venoms from spiders, reptiles, insects, and even mammals.
If you have not had a chance to check out Primal, it comes highly recommended as a DCC-type adult animated series. And by "adult" I do not mean risqué, I mean that it deals with strong themes and violence. Anyway, the second episode is River of Snakes, and despite being drawn almost cartoonishly, the sense of horror is effective.
As with the previous swarm, you can find potential venom effects in Appendix P of the core rulebook or in 50 Fantastic Functions For The D50. Or you could simply choose to have a DC 5 Fort save to avoid an additional 1d4 damage. Spider swarms are not going to have webs strong enough to capture PCs, but they may impede vision or slow characters down.
For other versions of the spider swarm, see Tales From the Magician's Skull #1 and Both Foul and Deep.
These turtles can apparently leap up from the water, and I am tempted to give them an extra ability where a hit requires a DC 5 Will save to avoid fainting for 1d5 rounds.
As with piranha swarms, the easiest way to deal with these is to get out of the water if you can. Easier said than done if you are trekking through a swamp. Needless to say, although turtles can bite - and snapping turtles can sever digits - being attacked by a swarm of turtles isn't something you need to worry about in real life. Well, all of these stats are a bit more gamist than realist.
If your swarming turtles are not large, snapping-turtle types, consider reducing the damage to 1d3 or even lower. Turtles with softer shells might even have a lower AC.
For some reason, swarms in these covers love attacking anyone who ventures into the water, even if the creatures attacking are not normally aquatic. Nonetheless, in a world where some might bond with Mulferret, Queen of Weasels, things like this just might happen. In fact, I think I included weasel swarms in her write-up, and as I do not have the book in front of me at the moment, they may be different.
Final Note - Swarm Criticals and Fumbles
When a swarm rolls a "20", that is a crit against everyone. That is, perhaps, a bit over the top and breaks suspension of disbelief just a little. I recommend that, if a swarm rolls a "20", each character is given a Luck check to avoid the critical effect. Each character who fails has a critical effect rolled, so that everyone is not always the recipient of the same effect.
When a swarm rolls a "1", that would be a fumble in all of its attacks. Rather than trying to figure out what that means, consider having the swarm just break of its attacks and/or disperse. A 5% chance per round of getting out of a swarm attack alive, just by luck, might not be realistic, but it is true to the nature of pulp fiction.
