CALCBIOME — ANT COLONY SIZE

How many workers in your colony?

Can’t count them all? Count part of them: the calculator estimates the total with the methods researchers use.

2 METHODSPartial count or mark–recapture.
RANGEA confidence interval, not a random guess.
PRIVATEFree, no account. Your settings stay on your device.

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Your count

Result

Counting a colony: the basics

Small colony: under 100 workers, count them directly on a photo, ticking each ant.
Partial count: draw a grid over a photo of the nest, count a few random squares, then multiply the average by the number of occupied squares.
Mark–recapture: mark a group of workers, release them, then count how many marked ones turn up in a second group.
Always an estimate: colonies are often bigger than they look, because part of them stays hidden.
Brood (eggs, larvae, pupae) is counted separately: it does not count as workers.

Mark–recapture examples

Marked	Caught	Marked recaptured	Estimate	95% range
20	20	5	72	35–111
50	40	10	189	108–270
100	100	20	484	323–645
200	150	30	978	700–1256

Published statistical methods. The result depends on how well you count: pick areas at random and respect the mark–recapture assumptions.

How we calculate

Partial count: estimate = (ants counted ÷ areas counted) × occupied areas in total.
Mark–recapture (Chapman): N = (M + 1)(C + 1) ÷ (R + 1) − 1, rounded down, where M = ants marked, C = ants caught on the 2nd pass, R = marked ants recaptured.
95% range = N ± 1.96 × √V, with V = (M + 1)(C + 1)(M − R)(C − R) ÷ [(R + 1)²(R + 2)]. The low end is never below the number of ants seen (M + C − R).

Example

50 workers marked, 40 caught the next day, 10 of them marked: N = 51 × 41 ÷ 11 − 1 = 189 workers, 95% range 108 to 270.

Sources: D. G. Chapman (1951), Seber variance (R package recapr); Billick (1999, Insectes Sociaux 46: 256–260), mark–recapture on Formica neorufibarbis, close to full excavation counts; Tschinkel (1988), subsample counts in Solenopsis; Robson & Regier (1964) for the 7-recapture minimum.

Frequently asked questions

How do I count the ants in my colony?

Under 100 workers, count them on a photo. Above that, count a few random areas and scale up, or use mark–recapture.

Does mark–recapture work for ants?

Yes, if marked ants mix well with the rest of the colony: a study on Formica found results close to a full count. If you only mark foragers, you mostly estimate the foragers.

How many ants should I mark?

Enough to recapture at least 7 on the second pass. For a colony of a few hundred workers, marking 30–50 ants is often enough.

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