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We have found that collisional loss of ultracold 6Li2 molecules can be determined by physics beyond universal long-range van der Waals interactions [1]. Starting with a degenerate Fermi gas of 6Li produced by sympathetic cooling with bosonic 23Na, we form Li2 molecules by a magnetic field sweep around a narrow Feshbach resonance. The resulting molecules are in the highest vibrationally excited state of the singlet potential, and decay via two-body collisions with other Li2 molecules, Li atoms, or Na atoms. We find that Li2+Li2 and Li2+Na collisions are well-described by a simple, universal quantum Langevin model, which assumes a unit probability of loss at short range due to a large number of available exothermic exit channels there, leaving rates dependent only on the long-range van der Waals interaction between collision partners [2]. In contrast, Li2 + Li collision rates are found to be exceptionally small, with an upper bound ten times smaller than the universal model prediction. This can be explained using a full close-coupling quantum calculation, and is a consequence of the exceptionally low density of available exit channels in this system consisting of the lightest alkali atoms [3]. Our work is the first example of collisions involving ultracold molecules with loss determined by physics beyond universal long-range van der Waals interactions. It points the way towards more interesting examples of ultracold chemistry that depend on the details of short-range interactions, such as scattering resonances or reactivity determined by matrix elements between quantum states. The work also addresses a long-standing puzzle in the field of ultracold Fermi gases, of unexpectedly long lifetimes of molecules formed around the narrow Feshbach resonance in 6Li [4]. We find that the lifetimes of these molecules are short, as expected.