This can happen naturally in some ant species.
Ants have three major body regions: the head, thorax, and abdomen. The abdomen contains important internal organs, and in some species its size and shape can vary considerably.
Some ants have workers with specialized body forms.
Others have reproductive individuals that are substantially larger than ordinary workers.
There are also ants in which certain individuals become highly specialized for storing liquid food.
These are sometimes called repletes.
Replete ants can have dramatically swollen abdomens because they function as living food-storage vessels for their colonies.
They receive liquid food from other workers and store it internally, allowing the colony to access that reserve later.
This is one possible explanation for unusually rounded ants seen in photographs—but the exact species shown in the viral image cannot be confirmed from the picture alone.
There are many other possibilities.
The insects could represent reproductive individuals.
They could belong to a species with naturally enlarged abdomens.
The photograph could also exaggerate their apparent size because of close-up photography.
Macro photography can make relatively small insects appear enormous.
A tiny ant photographed from only a few centimeters away can look almost monstrous when displayed on a large screen.
This is one reason viral wildlife photographs can create misleading impressions.
The viewer sees an enlarged image and unconsciously interprets the insect as physically enormous.
But the actual animal may be much smaller.