What kind of game this is
Swarm Simulator is a page of text and numbers with no pictures in it at all, and it is one of the cleanest things this genre has produced. You are a swarm of insects. Drones eat meat. Meat buys more drones. Then a queen appears, and the queen does not gather meat: she produces drones. Then a nest produces queens, a greater queen produces nests, and the game's whole shape is visible.
The chain runs eleven tiers deep, from drones through queens, nests, greater queens, hives, hive queens, empresses, prophets, goddesses, pantheons and overminds. Each tier produces the one below it, so buying anything high up rewrites the growth curve of everything underneath. Larvae sit underneath all of it as the currency you morph into new adults, so the actual limiting resource keeps moving as you climb.
The prose is dry and the joke is the escalation. You start counting individual drones and end up reading a number with a suffix you have not seen before, still described in the same flat sentences about your swarm eating.
Meat, territory and energy
There are three columns, and they are three separate economies that need each other.
Meat is the production tree described above. Territory is the military tree: swarmlings, stingers, spiders, mosquitoes, locusts, roaches, giant spiders, centipedes, wasps, devourers and worse, which capture territory rather than gather meat, and territory in turn fuels expansion. Energy is the third, capped and slowly refilling, and it is spent on abilities rather than on units. Nexus increase how much energy you can draw on, and each nexus costs more than the last, with a hard ceiling on how many your spellcasters can use.
That last one is the design decision that makes the game more than a spreadsheet. Energy is scarce and it is also the currency you must pay to leave, which means every ability you cast is a delay to your next reset.
Ascension
The reset is called ascending, and the game explains it in its own words: to activate mutagen your swarm must restart on a new world, because space travel is too harsh for most of your swarm and only a few larvae survive strengthened. Ascending costs energy. Crucially, the cost falls the more energy you have already spent on other things during the run, so the game actively pays you for using your abilities rather than hoarding them for the exit.
What you get is mutagen, which makes every member of the next swarm stronger, and a count of how many worlds you have infested. Crystals, a frozen form of energy with no cap, also survive ascension. Most of the mid game is a rhythm of push, spend, ascend, arrive faster.
There are 121 achievements and 179 upgrades in the game's own data tables, which is a reasonable measure of how much is behind that loop.
Offline progress, which it does properly
Close the tab and come back and the game tells you how long you were away and exactly what your swarm produced in that time. This is real offline calculation, not a token bonus, and it makes Swarm one of the better games here to check on twice a day rather than watch.
Controls, and the phone question
You click buy buttons and you type numbers into a quantity box. That is the entire interface. The page ships a viewport meta tag and the layout is three plain columns of text, so a phone handles it better than most games in this catalogue, though the number formatting gets cramped and you will do a lot of scrolling. Perfectly usable on a phone, still better on a desktop.
Saves live in your browser. There is an export in the settings, and the original Kongregate release had a save sync server, but on the main site your progress is local, so clearing site data ends the run.
How long it takes
The hundred hours in this page's data is our judgement, not a measured figure, and there is no HowLongToBeat entry for it. Databases that bucket idle games by length put Swarm in the weeks bracket rather than the months bracket, which matches the feel: the tiers run out eventually, and a determined player sees most of the game in a season rather than a year.
Getting further
Buy the highest tier you can afford, always, before topping up the lower ones. The tree does the rest.
Spend your energy rather than saving it. The ascension cost drops as you spend, so hoarding it makes the reset more expensive, not less.
Ascend before the run stops moving. The first ascension feels premature and is not.
Who made it, and where to play
Swarm Simulator is by Evan Rosson, who describes it on his own site as a text-only browser-based idle game. The repository dates from August 2014, which makes it one of the older games we list. Play it free at swarmsim.com. The game sells optional crystal packs; nothing else costs money.
The source is on GitHub under GPL version 3. That licence would let us serve a copy, and we may yet, but the project is built from CoffeeScript and AngularJS 1.x with tooling that has been dead for years, so it is not a build we will put in front of readers until it has been made and checked properly.
One clarification worth making, because search results confuse them. Swarm Simulator: Evolution, the free 3D game on Steam and on phones, is by Scary Bee LLC, not by Rosson. He says on his own site that the Android and iOS versions are based on his game, with much prettier graphics, but they are somebody else's product. This page is about the original.