What was found
Researchers removed egg sacs from fertilised female Pardosa lugubris and offered them unrelated sacs of the same age. Across the tested one-, two-, and three-day-old sacs, every deprived female adopted the foreign sac.
When females were offered their own sac and another female's sac at the same time, they selected whichever one they encountered first and did not later swap it. Unfertilised females did not adopt the offered sacs.
More than a behavioural response
The researchers also measured heat-shock proteins and reactive oxygen species. Removing egg sacs or juveniles produced changes in physiological stress markers in mothers and offspring, and some of those responses declined over time.
Why it matters
The results suggest a powerful maternal state that does not depend on recognising individual offspring. Adoption may maintain caregiving behaviour after reproductive loss, but the study does not establish human-like grief or reveal what a spider experiences subjectively.
That distinction does not make the finding less remarkable. It makes it clearer: offspring loss measurably affects both behaviour and physiology in an invertebrate whose parental care is easy to underestimate.